Public Health & Epidemiology

Start with populations and measures of disease. Learn study designs, bias, and screening before outbreak investigation and prevention, then connect interventions to environmental conditions, health systems, and ethics.

Population Health and Measurement

Define populations, health outcomes, and the measures used to describe them.

Public Health Foundations

• Public health — organized efforts to prevent disease, prolong life, and improve health at the population level. Its tools include surveillance, policy, environmental protection, health promotion, and delivery of preventive services.

• Population health — the distribution of health outcomes within a defined population and the factors that shape that distribution. It concerns both average health and inequalities between groups.

• Epidemiology — the study of the distribution and determinants of health-related states or events in specified populations and the application of that study to health problems. Its classic examples include John Snow’s Broad Street cholera investigation, the Hill criteria, and compartmental models such as susceptible-infected-recovered frameworks.

  • epidemics — Epidemics are outbreaks in which an infectious disease spreads rapidly through a population over a wide area. They are often modeled with susceptible-infectious-recovered frameworks and analyzed using the basic reproduction number R0.

  • infection — Infection is the spread of disease through a host population, whether by vectors, fomites, or direct transmission. In epidemiological models such as SIR, it is described by the force of infection and by quantities like R-naught and multiplicity of infection.

  • epidemiology methods

    • Bradford Hill criteria — The Bradford Hill criteria are a set of considerations used in epidemiology to judge whether an observed association may be causal. They include ideas like temporality, biological gradient, plausibility, and coherence.

• Biostatistics — statistical reasoning and methods applied to biological, clinical, and public-health data. It supports design, measurement, inference, prediction, and communication of uncertainty.

• Social determinants of health — social, economic, political, and environmental conditions that influence exposure, vulnerability, resources, and access to care across the life course.

• Health inequity — a systematic difference in health judged to be avoidable and unjust. Description of a disparity alone does not establish its cause or identify the intervention that will reduce it.

• One Health — a collaborative approach recognizing connections among human, animal, and environmental health, especially for zoonoses, antimicrobial resistance, food systems, and ecosystem change.

• Health in all policies — evaluates health consequences across sectors such as housing, transportation, education, agriculture, labor, and climate rather than treating health as the concern of medical care alone.

• Essential public-health services — a framework for assessing population health, investigating hazards, communicating, building partnerships, creating policy, assuring equitable access, maintaining infrastructure, and improving performance.

• Health equity — a condition in which everyone has a fair opportunity to attain health and no group is systematically disadvantaged by avoidable social arrangements.

• Population strategy of prevention — shifts the distribution of risk across a whole population. A small average change can prevent more cases than an intensive intervention limited to a small high-risk group.

• Health literacy — the ability of people and organizations to find, understand, evaluate, and use health information and services. It depends on communication and system design, not individual skill alone.

• Community health assessment — combines quantitative data, lived experience, assets, needs, and stakeholder priorities to describe local health and select action areas.

• Planetary health — studies how human health depends on natural systems and how environmental change driven by human activity feeds back into health, livelihoods, and inequality.

Measuring Disease and Health

• Counting Events and Time at Risk

  • Case definition — a standard set of clinical, laboratory, person, place, and time criteria used to classify cases for surveillance or investigation. Surveillance definitions prioritize consistency and need not equal clinical diagnostic rules.

  • Count, proportion, ratio, and rate — a count is a number of events; a proportion has a numerator contained in its denominator; a ratio compares quantities; a rate incorporates population at risk and, in a true incidence rate, person-time.

  • Person-time — sum of time each eligible person remains under observation and at risk. It accommodates unequal follow-up but does not describe how risk changes within that time.

  • Incidence proportion — the proportion of an initially disease-free population that develops an outcome during a specified period. It is also called cumulative incidence or risk.

  • Incidence rate — new events divided by accumulated person-time at risk. Its unit is events per unit of person-time rather than a probability.

  • Prevalence — the proportion of a population with a condition at a point or over a period. It reflects both incidence and duration and can rise when survival improves even if incidence does not.

  • Mortality rate — deaths in a defined population over time. Cause-specific rates use deaths from a stated cause in the numerator; case fatality compares deaths among diagnosed cases.

  • Crude rate — the observed event rate in an entire population without standardization. It represents actual population burden but may be misleading for comparisons when group compositions differ.

• Comparing Risks and Rates

  • Risk difference — risk in one group minus risk in another. It measures absolute excess or reduction and is often central to population impact.

  • Risk ratio — risk in an exposed or treated group divided by risk in a comparison group. A relative effect must be interpreted alongside baseline risk.

  • Odds ratio — the ratio of two odds. It equals the exposure-outcome cross-product ratio in a two-by-two table and can approximate a risk ratio when the outcome is rare under suitable sampling.

  • Rate ratio — incidence rate in one group divided by the rate in another. It compares event occurrence per person-time.

  • Attributable fraction — estimates the proportion of events among an exposed group, or in a population, associated with an exposure under causal assumptions. It combines effect and exposure prevalence.

  • Age standardization — applies age-specific rates to a common reference population so groups with different age structures can be compared. Standardized rates are comparative summaries, not observed crude rates.

  • Standardized mortality ratio — observed deaths divided by deaths expected after applying reference rates to the study population’s strata. It compares with a reference but is not directly comparable across differently structured study populations.

• Survival and Population Burden

  • Survival function — probability of remaining free of the event beyond a given time. Censoring methods require assumptions about why follow-up ended.

  • Hazard — instantaneous event rate among those still event-free at a given time. A hazard ratio is a relative rate, not a ratio of cumulative risks or survival probabilities.

  • Life expectancy — the mean remaining years implied by a life table’s age-specific mortality rates. Period life expectancy applies current rates hypothetically and is not a forecast for an actual birth cohort. It is a common demographic measure that can fall sharply during war or epidemic, as in examples from Syria and Rwanda.

  • Disability-adjusted life year — a population burden measure combining years of life lost and years lived with disability. Its weights and assumptions make it a policy metric, not a direct biological quantity.

  • anthropometric measures
    • body mass index — Body mass index is a weight-for-height measure defined as kilograms divided by meters squared, or as a person’s weight divided by the square of their height. It is commonly used as a rough screening tool to classify underweight, normal weight, overweight, and obesity, and for threshold-based health assessments, though it is often criticized for crude assumptions.
  • Disease prevalence
    • endemic diseases — Endemic diseases are infections that remain at a roughly constant baseline level in a population over time. Unlike epidemic outbreaks, they persist when each infected person transmits the disease to about one new person on average.

Descriptive Epidemiology and Surveillance

• Describing and Finding Cases

  • Person, place, and time — the core dimensions used to describe who is affected, where events occur, and how patterns change. Description generates hypotheses but does not alone identify causes.

  • Endemic, epidemic, and pandemic — endemic describes expected ongoing occurrence in a population; epidemic is occurrence above an expected level; pandemic is an epidemic spreading across countries or continents with sustained transmission.

  • Epidemic curve — plots cases by time of symptom onset or another event. Its shape can suggest point-source, continuous, intermittent, or propagated transmission but must be combined with exposure and contact evidence.

  • Case finding — systematic identification of people meeting a case definition through reports, records, laboratory data, interviews, or active outreach.

  • Line list — one-row-per-case table containing identifiers or codes, classification, onset, exposures, laboratory results, location, contacts, and outcomes needed for an investigation.

  • Notifiable disease — a condition that law or regulation requires designated parties to report to health authorities. Lists and reporting duties vary by jurisdiction.

• Surveillance Systems and Their Performance

  • Public-health surveillance — ongoing, systematic collection, analysis, interpretation, and dissemination of health data for action.

  • Passive surveillance — relies on routine reporting by clinicians, laboratories, or institutions. It is relatively inexpensive but often incomplete and sensitive to reporting practices.

  • Active surveillance — public-health staff seek cases directly from reporting sources. It can improve completeness during outbreaks or elimination programs but requires more resources.

  • Sentinel surveillance — selected sites provide detailed or timely information. It can detect trends but may not represent an entire population without a suitable design.

  • Syndromic surveillance — monitors symptom patterns or proxies before diagnoses are confirmed, such as emergency-department complaints. Speed is gained at the cost of specificity.

  • Wastewater surveillance — measures biological or chemical markers in community wastewater to track population-level trends without requiring individual clinical testing. Catchment, flow, decay, and laboratory methods affect interpretation.

  • Surveillance sensitivity — proportion of events meeting the surveillance target that the system detects. Changes in testing or reporting can alter sensitivity and create artificial trends.

  • Surveillance timeliness — speed from event occurrence through detection, reporting, analysis, and action. A complete system can still fail its purpose if information arrives too late.

  • Surveillance representativeness — how well reported events describe occurrence across people, places, and time. Participation and care access can produce systematic gaps.

Study Design and Causal Reasoning

Connect study design and causal questions to possible sources of bias.

Study Designs

• Observational Designs

  • Case report and case series — detailed descriptions of one or several patients without a comparison group. They can identify new phenomena but cannot estimate comparative effects reliably.

  • Cross-sectional study — measures exposure and outcome at one time or over a short window. It estimates prevalence and associations but often cannot establish temporal order.

  • Case-control study — begins with cases and controls and compares prior exposures. It is efficient for rare outcomes; the odds ratio estimates the sampling-compatible association when controls represent the exposure distribution in the source population.

  • Cohort study — follows exposed and unexposed groups, prospectively or through records, to compare outcome occurrence. Loss to follow-up and time-varying exposures require careful handling.
    • Cohort studies
      • Cardiovascular cohort studies
        • Framingham Heart Study — The Framingham Heart Study is the long-running Massachusetts cohort study founded in 1948 to track the causes of cardiovascular disease. It later expanded to include descendants and produced the Framingham Risk Score for estimating ten-year heart-disease risk.

  • Ecologic study — compares group-level exposures and outcomes. Associations at the group level need not hold among individuals, a problem known as the ecological fallacy.

  • Nested case-control study — samples cases and controls from an established cohort, preserving the cohort’s temporal structure while reducing the cost of measuring stored exposures.

  • Case-cohort study — compares all cohort cases with a randomly selected subcohort that can serve as the comparison group for multiple outcomes.

  • Case-crossover study — compares a person’s exposure shortly before an acute event with that same person’s exposure during control periods, controlling stable individual characteristics by design.
• Experiments, Natural Experiments, and Evidence Synthesis

  • Randomized controlled trial — assigns interventions by a random mechanism. Randomization supports exchangeability in expectation, while allocation concealment, adherence, attrition, blinding, and outcome measurement still affect validity.

  • Cluster-randomized trial — randomizes groups such as clinics, schools, or communities. Analysis and sample-size calculations must account for correlation within clusters.

  • Stepped-wedge trial — clusters cross from control to intervention at randomized times until all receive it. Secular trends and within-cluster correlation require explicit modeling.

  • Natural experiment — studies an exposure change driven by policy, environment, or another process outside investigator assignment. Causal strength depends on the assignment mechanism and comparison strategy. It is an observational research design in which outside events or policies create a treatment-like change that researchers do not assign themselves. It is used when exogenous variation approximates random assignment, as in Card and Krueger’s minimum-wage study.

  • Interrupted time-series study — estimates whether an outcome’s level or trend changes after an intervention using repeated observations before and after it. Concurrent events and time-varying measurement remain threats.

  • Systematic review — uses prespecified methods to identify, appraise, and synthesize evidence addressing a focused question. A meta-analysis is a statistical synthesis and is neither required nor automatically valid when studies differ materially.

Bias, Confounding, and Causal Reasoning

• Selection and Information Bias

  • Selection bias — the analyzed relationship differs from the target relationship because inclusion, retention, or observation depends on causes of exposure and outcome. Selection bias is a statistical error that occurs when the sample observed does not represent the target population, often because inclusion or retention depends on the variables being studied. Sampling bias and volunteer bias are standard subtypes. Conditioning on study entry, retention, measurement, or analysis can create associations that differ from the target population relationship.

  • Information bias — systematic error in measuring exposure, outcome, or covariates. Recall bias, interviewer effects, diagnostic suspicion, and imperfect records are common mechanisms.

  • Recall bias — accuracy or completeness of remembered exposure differs between comparison groups, often because outcome experience changes attention or reporting.

  • Loss-to-follow-up bias — the observed cohort differs causally from the target because retention depends on variables related to exposure and outcome.

  • Healthy-worker effect — employed populations often have lower overall mortality than the general population because severely ill people are less likely to enter or remain employed.

  • Immortal-time bias — a period during which an outcome could not occur under the exposure definition is incorrectly credited to the exposed group.

  • Nondifferential misclassification — measurement error has the same classification probabilities across comparison groups under a specified condition. It does not universally bias effects toward the null.

  • Differential misclassification — measurement quality differs according to exposure, outcome, or another analysis variable, allowing bias in either direction.

• Causal Structure and Sensitivity

  • Confounding — distortion of an exposure-outcome comparison by shared causes. Adjustment should follow a causal model; automatically controlling every measured variable can introduce bias.

  • Residual confounding — confounding that remains after adjustment because causes were unmeasured, poorly measured, incorrectly modeled, or grouped too coarsely.

  • Collider bias — conditioning on a common effect of two variables can create a noncausal association between them. Selection into hospitals, tested populations, or complete-case samples can act as collider conditioning.

  • Mediation — a mediator lies on a causal path from exposure to outcome. Estimating direct and indirect effects requires stronger assumptions than estimating a total effect.

  • Reverse causation — an outcome or its preclinical process influences the measured exposure. Temporal information and design are needed to distinguish this from forward causation.

  • Effect-measure modification — an effect differs across levels of another variable on a stated scale. It is a property to describe, not a bias to remove automatically.

  • Negative control — an exposure or outcome chosen because a proposed causal mechanism predicts no effect. An observed association can reveal residual bias, though a null result does not prove the main estimate unbiased.

  • Sensitivity analysis — quantifies how estimates change under alternative assumptions about measurement, missingness, model choice, or unmeasured confounding.

Screening and Outbreak Investigation

Distinguish screening from diagnosis and follow outbreak investigation.

Screening and Diagnostic Testing

• Test Performance and Interpretation

  • Sensitivity — the probability a test is positive among people who have the target condition. It is a property of the test in a population and protocol, not an unconditional constant.

  • Specificity — the probability a test is negative among people who do not have the target condition. Specificity is the probability that a test correctly returns negative for people without the condition. It is the complement of the false positive rate and is contrasted with sensitivity, the true positive rate.

  • Positive predictive value — the probability of the condition among people with a positive result. It depends strongly on prevalence as well as sensitivity and specificity.

  • Negative predictive value — the probability of not having the condition among people with a negative result. It also changes with prevalence and setting.

  • Likelihood ratio — compares the probability of a test result among people with and without a condition. Positive and negative likelihood ratios update pretest odds to post-test odds.

  • Receiver operating characteristic curve — plots sensitivity against one minus specificity over thresholds. Area under the curve measures ranking discrimination and does not determine calibration, clinical value, or a preferred threshold.

  • Pretest probability — estimated probability of a condition before the new test result, based on prevalence, symptoms, history, and setting. It anchors interpretation of likelihood ratios and predictive values.

  • Diagnostic threshold — score or measurement boundary used to classify results. Moving it usually trades sensitivity against specificity and changes downstream workload and harm.

• Screening Programs and Their Biases

  • Screening — testing people without recognized symptoms to identify elevated risk or early disease. Benefit depends on disease natural history, test performance, effective follow-up, treatment benefit, harms, access, and overdiagnosis.

  • Screening interval — time between repeated screens. It should reflect disease progression, test sensitivity, prior results, treatment benefit, burden, and competing harms.

  • Lead-time bias — earlier detection lengthens measured survival from diagnosis without delaying death.

  • Length bias — periodic screening preferentially detects slower-progressing disease because it remains detectable longer.

  • Overdiagnosis — detection of a condition that would not have caused symptoms or death during a person’s lifetime. It is distinct from a false-positive test.

  • Verification bias — the reference diagnosis is obtained preferentially for people with certain index-test results, distorting estimated test performance.

  • Spectrum effect — test performance changes with disease severity, comorbidity, demographics, and alternative diagnoses, so estimates from selected cases and healthy controls may not transport to practice.

Outbreak Investigation and Infectious Disease

• Investigating Spread

  • Outbreak investigation — commonly includes verifying the diagnosis, defining and finding cases, describing person-place-time patterns, developing and testing hypotheses, implementing controls, and communicating findings. Control measures may begin before every analytic step is complete.

  • Index case and primary case — an index case is the first case recognized by investigators; a primary case is the person who introduces infection into a group. They need not be the same person.

  • Incubation period — time from infection to symptom onset. The latent period runs from infection to becoming infectious and can be shorter or longer than incubation. It is used in epidemiology for diseases such as influenza, rabies, and typhoid, where symptoms may not appear for days or weeks.

  • Infectious period — interval during which an infected host can transmit an agent. It need not match either symptom duration or test positivity.

  • Serial interval — time between symptom onset in an infector and symptom onset in a person they infect. It can be negative when presymptomatic transmission occurs.

  • Generation interval — time between infection of an infector and infection of a secondary case. It is usually unobserved and inferred from linked cases and timing data.

  • Basic reproduction number — the expected secondary cases generated by a typical infectious person in a wholly susceptible population under specified conditions. It is not a fixed biological constant. Commonly denoted R0 (R-naught/R-zero; also R-nought), it is a key epidemic threshold parameter in SIR models, with outbreaks declining when it falls below 1. It is used in next-generation-matrix calculations and in estimating herd-immunity thresholds and endemic equilibrium.

  • Effective reproduction number — expected secondary cases under current immunity, behavior, interventions, and contact patterns. Values below one imply declining transmission on average.

  • Attack rate — cumulative incidence during an outbreak, often within a defined exposed group. A secondary attack rate measures spread among susceptible contacts of primary cases.

  • Reservoir — the habitat in which an infectious agent normally lives and multiplies. A vector transmits an agent between hosts; a vehicle is a nonliving medium such as food or water.

  • Herd protection — indirect protection produced when immune individuals reduce opportunities for transmission. Threshold calculations from simple homogeneous models can fail under clustered contact, waning immunity, or variant change.

  • Contact tracing — identifies and supports people exposed to a case so they can test, monitor, receive prophylaxis, isolate, or quarantine as appropriate.

  • Genomic epidemiology — combines pathogen sequence variation with time, place, contact, and sampling information to investigate transmission and evolution. Genetic similarity alone does not prove direct transmission.

  • Superspreading — highly uneven transmission in which a minority of infections generate many secondary cases. Biology, behavior, timing, setting, and network structure can all contribute.

  • Compartmental models
    • SIR model — The SIR model is the classic compartmental model of epidemiology that divides a population into susceptible, infected, and recovered or removed groups. It underlies basic outbreak calculations such as R-naught and was extended by adding an exposed state in SEIR models.
  • epidemic terms
    • Pandemic — A pandemic is a disease outbreak that spreads across multiple continents or worldwide, as modeled by the SIR framework and contact tracing. The term also titles a board game about containing outbreaks, cures, and research facilities.
  • epidemiologists
    • Austin Bradford Hill — Austin Bradford Hill was the epidemiologist whose criteria are used to judge whether an observed association is likely causal. He also helped show that smoking caused lung cancer and led an early randomized trial of streptomycin for tuberculosis.
• Outbreaks, Pandemics, and Disease Examples
  • infectious diseases
    • COVID-19 — COVID-19 is the disease caused by the coronavirus SARS-CoV-2, whose 2020 pandemic disrupted travel, concerts, and public life worldwide. Typical clues mention spike proteins, ACE2 receptors, variants such as Delta and Omicron, and diagnostic tests like RT-PCR.
  • infectious disease outbreaks

    • a plague — A plague is a major epidemic disease outbreak, often used for historical outbreaks such as the one that reached Constantinople from Pelusium in the reign of Justinian. The term also evokes the Black Death, whose devastation in the 1340s helped reshape European society.

    • plagues — A plague is a widespread outbreak of infectious disease, often used in mythology and literature to describe devastating epidemic events. Clues point to famous ancient and literary examples such as the Plague of Athens, the Antonine plague, and Camus’s The Plague.

  • epidemic outbreaks

    • 1793 Philadelphia yellow fever epidemic — The 1793 Philadelphia yellow fever epidemic devastated the city while Benjamin Rush and other residents struggled to treat the sick. It also formed the backdrop for Charles Brockden Brown’s Arthur Mervyn and for efforts by Richard Allen and Absalom Jones to aid Black workers.

    • 1793 yellow fever epidemic in Philadelphia — The 1793 yellow fever epidemic in Philadelphia killed many residents and drove George Washington out of the city for the summer. Richard Allen, Absalom Jones, Benjamin Rush, and Stephen Girard are all tied to responses to the outbreak.

    • pandemics — Pandemics are widespread disease outbreaks, such as the Black Death and modern global epidemics. Historical responses to them included quarantines, lazaretti, and plague doctors’ bird-beak masks.
      • influenza
        • Spanish flu pandemic — The Spanish flu pandemic was the major 1918 influenza outbreak that spread globally during the final year of World War I. Its name comes from Spain’s uncensored reporting during wartime, while the disease itself killed tens of millions of people worldwide. It was linked to the H1N1 strain and prompted public-health responses such as anti-spitting campaigns in cities like New York.
    • plague — Plagues are major outbreaks of disease that have repeatedly devastated societies, from the Antonine Plague to Justinian’s plague and the Black Death. Ancient and medieval accounts often tie them to mass death, conversion, and social collapse.

      • Bubonic plagues — Bubonic plagues are outbreaks of plague disease that repeatedly devastated Europe, with the Black Death as the most famous example. Their demographic effects reshaped labor conditions and inspired chronicles, treatises, and religious responses such as the Flagellants.

      • Plague of Justinian — The Plague of Justinian was the great early medieval bubonic plague pandemic associated with Yersinia pestis and the reign of Justinian. It devastated the Byzantine world in the sixth century, with Constantinople suffering catastrophic mortality and later outbreaks recurring across the medieval eastern Mediterranean.

      • the plague of Justinian — The Plague of Justinian was the mid-sixth-century pandemic that ravaged the Byzantine Empire under Justinian. It was an early major European outbreak of Yersinia pestis, with origins traced to Egypt and possibly farther east.

    • SARS — SARS, or severe acute respiratory syndrome, is a coronavirus disease that caused a major 2002–2003 outbreak centered in Guangdong Province, China, and sparked international fear and concern, especially around the Pacific Rim and in Canada. It was described as a near-pandemic that disrupted travel, business, and sporting events in 2003. The disease was studied through antiviral and interferon-based treatments and was linked to an unknown coronavirus.
  • Influenza
    • influenza viruses — Influenza viruses are orthomyxoviruses with segmented negative-sense RNA genomes. Their hemagglutinin and neuraminidase proteins determine strains such as H1N1 and H5N1, and the viruses are responsible for major pandemics including the Spanish flu.
  • influenza outbreaks
    • Swine flu — Swine flu is an influenza outbreak famously associated with the 1976 U.S. vaccination campaign and the fear of a pig-to-human virus. The episode became notorious because the vaccine response created more harm and controversy than the disease itself.
  • Influenza pandemics

    • Spanish flu — The Spanish flu was the devastating 1918-1919 influenza pandemic at the end of World War I, caused by an H1N1 virus and killing tens of millions worldwide. Wartime censorship in Europe helped make it seem especially associated with Spain, where the uncensored press first drew wider attention to the outbreak; it spread through military and naval routes, including Camp Funston, Fort Riley, and the Philadelphia parade. It was unusually lethal for healthy adults, is often linked to cytokine storm, and is remembered for a deadly second wave. It devastated places such as Samoa and Inuit communities, and a recovered viral genome was obtained from permafrost.

    • Spanish flu epidemic — The Spanish flu epidemic was the deadly 1918 influenza pandemic that spread worldwide near the end of World War I. It was long associated with influenza rather than bacteria, and its name reflects wartime censorship that distorted reporting in neutral countries. Common clues include the death of figures such as Guillaume Apollinaire and Gustav Klimt, along with King Alfonso XIII surviving the outbreak.

  • plague outbreaks
    • Bubonic plague outbreaks — Bubonic plague is the disease behind the great historical outbreaks known as the Black Death and other major epidemics. Its transmission through fleas and its appearance in works about plague-ridden cities make it a standard reference point for medieval and modern disease history.
  • waterborne diseases
    • cholera — A water-borne intestinal diarrheal disease caused by Vibrio cholerae. Its toxin raises cAMP in intestinal cells, driving massive fluid loss and severe diarrhea and dehydration. It is spread through contaminated water and poor sanitation, and has caused deadly outbreaks in places such as Soho, colonial India, and in the Broad Street outbreak studied by John Snow. Treatment centers on oral rehydration, with zinc and vaccines also used.
  • Tuberculosis
    • Andrew Speaker — Andrew Speaker is an American man associated with a public tuberculosis quarantine case. He became known for being the first person quarantined by the U.S. government in more than forty years.
  • AIDS crisis — The AIDS crisis was the HIV/AIDS epidemic that devastated gay, queer, and artistic communities in the 1980s and 1990s. It inspired major activist art and memorials, including the NAMES Project memorial quilt, and artists such as Keith Haring and Nan Goldin responded through activism and exhibitions documenting loss and protest. Public awareness rose through speeches by figures such as Mary Fisher and Elizabeth Glaser, and it is also associated with Rock Hudson’s death.

    • AIDS denialism — AIDS denialism is the pseudoscientific rejection of the viral cause of AIDS and related antiretroviral treatments. It became politically influential in South Africa under Thabo Mbeki and was condemned by the Durban Declaration.

    • AIDS literature
      • And the Band Played On: Politics, People, and the AIDS Epidemic — And the Band Played On: Politics, People, and the AIDS Epidemic is Randy Shilts’s investigative book about the AIDS crisis. It criticizes the indifference of governments and the media to the spread of HIV in the 1980s.
    • Early AIDS cases
      • Gaëtan Dugas — Gaëtan Dugas was a French-Canadian flight attendant nicknamed Patient Zero in early AIDS narratives. He was described as the only common link among the first reported cases of the disease and was long assumed to have been an early carrier.
    • HIV transmission cases
      • Nushawn Williams — Nushawn Williams is the man convicted in connection with selling cocaine and with knowingly exposing multiple young women in Jamestown, New York, to HIV. He became notorious for transmitting AIDS to ten women under the age of twenty while already aware that he had the virus.
  • AIDS epidemic — The AIDS epidemic was a major public-health and cultural crisis. It drew activism from groups like ACT UP and left a large memorial footprint in the NAMES Project quilt. It became widely visible through figures such as Ryan White, Rock Hudson, Magic Johnson, and Mary Fisher, and through works like And the Band Played On. It also reshaped late-20th-century literature and drama in works by Thom Gunn, Tony Kushner, Larry Kramer, and Terrence McNally.

    • AIDS Patient Zero — AIDS Patient Zero was the misleading label attached to flight attendant Gaétan Dugas, who became entangled in early North American AIDS tracing narratives. He was associated with early CDC contact tracing and later scholarship argued against the myth that he introduced the disease to the United States.

    • And the Band Played On — And the Band Played On is Randy Shilts’s 1987 account of the early AIDS epidemic in the United States. It criticizes public-health officials and the Reagan administration for ignoring the crisis.

    • Dr. Jonathan Mann — Dr. Jonathan Mann led the World Health Organization’s AIDS program and was among the victims in the crash referenced by the clues. He was a public health official widely associated with global HIV/AIDS work.

    • Kimberly Bergalis — Kimberly Bergalis became a national symbol of the early AIDS crisis after alleging that she had been infected by her dentist. She testified before Congress in 1991 and died later that year in Florida.

    • The AIDS Memorial Quilt — The AIDS Memorial Quilt is a large commemorative project honoring victims of AIDS and was first displayed on the National Mall in 1987. Created by Cleve Jones, it later grew to tens of thousands of panels and became a major symbol of AIDS activism.

  • Ebola outbreaks
    • Kikwit — Kikwit is a town in the Democratic Republic of the Congo that became notorious for a 1996 Ebola outbreak. The epidemic drew attention for its high fatality rate and for public-health containment efforts.
  • mosquito-borne diseases

    • Dengue Hemorrhagic Fever — Dengue hemorrhagic fever is a mosquito-borne illness caused by dengue flaviviruses and associated with outbreaks across Southeast Asia, Africa, and the Americas. It can be confused with chikungunya and was noted in a Pakistan outbreak.

    • Zika virus — Zika virus is a mosquito-borne flavivirus first isolated in Uganda and later linked to outbreaks in Micronesia, French Polynesia, Brazil, and the United States. It is associated with microcephaly in fetuses and has also been tied to Guillain-Barré syndrome. Its spread is associated with Aedes mosquitoes, and AXL has been proposed as a receptor for the virus.

    • dengue — Dengue is a mosquito-borne viral fever spread chiefly by Aedes aegypti. It can cause severe joint pain, hemorrhagic complications, and dengue shock syndrome, and repeated infection can be worsened by antibody-dependent enhancement.
      • Dengue fever — Dengue fever is a mosquito-borne tropical disease caused by dengue virus and spread mainly by Aedes aegypti. It can produce severe forms such as dengue hemorrhagic fever and dengue shock syndrome, and it is often called breakbone fever because of intense joint and muscle pain.

    • West Nile virus — West Nile virus is a mosquito-borne flavivirus first identified in Uganda and later spread widely in North America. It can cause fever, rash, meningitis, and encephalitis, with birds such as crows and sparrows serving as important reservoirs.

    • yellow fever — Yellow fever is a mosquito-borne viral disease caused by flaviviruses and spread in its urban form by Aedes aegypti. It is associated with jaundice and a hemorrhagic phase, and with nineteenth-century epidemics in Philadelphia, Panama, and Havana. Related figures and milestones include Carlos Finlay’s vector theory, Walter Reed’s work, and the later vaccine strain developed by Max Theiler. The nickname yellow jack comes from the yellow quarantine flags once flown by infected ships.

    • Zika
      • Zika virus epidemic — The Zika virus epidemic was the 2015-2016 outbreak that raised international concern before the Rio Olympics. It was linked to mosquito control, congenital defects, and public-health warnings in Latin America.
  • Antimicrobial resistance — survival and spread of microbes under antimicrobial selection. Stewardship, infection prevention, diagnostics, vaccination, sanitation, and surveillance are complementary controls.

Prevention and Everyday Exposures

Connect prevention strategies to exposures and levels of intervention.

Prevention and Intervention

• Levels and Strategies of Prevention

  • Primordial prevention — prevents emergence of social or environmental conditions that create risk, such as policies shaping tobacco use, unsafe streets, or air pollution.

  • Primary prevention — acts before disease begins, including vaccination, safer environments, protective equipment, and reduction of harmful exposures.

  • Secondary prevention — detects and treats disease early, often through screening or case finding.

  • Tertiary prevention — reduces complications, disability, or recurrence after disease is established.

  • Quaternary prevention — seeks to prevent unnecessary medical intervention and harm from overmedicalization.

  • High-risk prevention strategy — targets people with elevated individual risk. It may offer favorable benefit-to-harm tradeoffs for recipients while preventing fewer total cases than a broad population shift.

  • Health promotion — supports people and communities in increasing control over determinants of health through information, environments, policy, and collective action.

  • Harm reduction — reduces adverse consequences of a behavior or exposure without requiring its immediate elimination. Examples include sterile-syringe services, naloxone access, and safer-use interventions. It is a public-health strategy often applied to drug use or sexual activity, and can include methadone clinics as well as other safer-use interventions.

    • Supervised injection facilities
      • Insite — Insite is Vancouver’s safe-injection site, often cited as the first supervised drug-consumption facility of its kind in North America. It appears in discussions of Vancouver’s harm-reduction policies, alongside the city’s downtown drug scene and public-health response to addiction.
    • supervised injection sites — Supervised injection sites are harm-reduction facilities where drug use is monitored to reduce overdoses and disease transmission. Examples include Vancouver’s Insite and other sites in North America, often paired with needle exchange programs.
• Vaccination and Communicable Disease Control
  • Vaccination — induces immune protection without the risks of natural infection. Program impact depends on effectiveness, coverage, timing, durability, access, and pathogen ecology. It is often done by injection of an attenuated or inactivated agent. Historical examples include Jenner’s smallpox work and Pasteur’s later vaccines; modern debates have included thimerosal and autism claims.

    • anti-vaccination — Anti-vaccination is the movement opposing immunization and other medical interventions that prevent infectious disease. Its modern popularity has been tied to Andrew Wakefield, thimerosal fears, and reactions to vaccine controversies such as Gardasil.

    • Anti-vaccination movement — The anti-vaccination movement rejects immunization and has been linked to resurgent outbreaks of diseases like measles. Recent clues tie it to Robert F. Kennedy Jr., Andrew Wakefield, and organized campaigns against vaccines and vaccine exemptions.

    • COVID-19 vaccines — COVID-19 vaccines are the immunizations developed against the coronavirus disease that emerged in Wuhan, including mRNA-based shots from Pfizer and Moderna. Examples mentioned in the clues include Sputnik V, AstraZeneca, BioNTech, and Johnson & Johnson, with the latter requiring only one dose.

    • smallpox vaccination
      • vaccination against smallpox — Vaccination against smallpox is the practice pioneered by Edward Jenner using cowpox material to protect against smallpox. It was later defended in Britain despite early opposition from critics such as pamphleteers attacking the procedure.
    • tuberculosis vaccines
      • Bacille Calmette-Guerin vaccine — The Bacille Calmette-Guerin vaccine is a live attenuated strain of Mycobacterium bovis used against tuberculosis. It provides limited protection for a few years and can cause lifelong positive tuberculosis skin tests.

    • vaccine — A vaccine is a preventive medical product that stimulates immunity against disease, famously including Jonas Salk’s polio vaccine and the campaign that helped eradicate smallpox. Vaccines may use weakened, inactivated, or engineered antigens, and public controversy has often centered on their safety and distribution.

    • Viral vaccines — Viral vaccines are immunizations designed to confer protection against viral infections. Examples include smallpox vaccination and the major array of vaccines developed by Maurice Hilleman.

  • Isolation and quarantine — isolation separates people known or suspected to be infected; quarantine restricts movement of exposed people during a possible incubation period. Legal authority and terminology vary by jurisdiction.

  • Disease eradication
    • eradicating smallpox — This was the global campaign to eradicate smallpox, coordinated by leaders such as Donald Henderson after Viktor Zhdanov proposed it in 1958. It relied on surveillance and containment, the bifurcated needle, and ring vaccination, and its success was certified in 1980.
  • Poliomyelitis
    • Polio prevention
      • Albert Sabin — Poliomyelitis is the viral disease that can cause paralysis and was famously associated with Franklin Roosevelt. Its prevention is tied to the Salk and Sabin vaccines, mass immunization campaigns, and the March of Dimes.
  • disease control measures
    • Quarantine — Quarantine is isolation of people or goods to prevent the spread of disease. The word originally referred to a forty-day waiting period, and it also had older legal senses involving a widow’s residence rights.
• Delivering and Evaluating Interventions

  • Program evaluation — asks whether an intervention was implemented, reached its intended population, changed intermediate outcomes, improved health, and produced unintended effects.

  • Efficacy and effectiveness — efficacy estimates benefit under controlled or ideal conditions; effectiveness estimates performance in routine settings with real uptake, adherence, delivery, and population diversity.

  • Number needed to treat — reciprocal of an absolute risk reduction over a specified time under compatible assumptions. It changes with baseline risk and should include uncertainty.

  • Health communication — designs and exchanges information so audiences can understand risk, options, uncertainty, and action. Trust, messenger, language, access, and two-way engagement affect impact.

  • Implementation evaluation — examines reach, adoption, fidelity, adaptation, dose, acceptability, cost, context, and sustainability to explain how an intervention operated in practice.

  • water fluoridation

    • fluoridation — Fluoridation is the practice of adding fluoride to public water supplies to reduce tooth decay. It was pioneered in places like Grand Rapids after studies of Colorado Brown Stain and is sometimes mocked in Cold War satire such as Dr. Strangelove.

Substance Use

• Alcohol use
  • drinking alcohol — Drinking alcohol is the act of consuming alcoholic beverages. It is associated with alcoholism and programs such as Alcoholics Anonymous, and in literature it is a recurring motif in works by Li Bai and Edwin Arlington Robinson, including Li Bai’s moonlit poems about drinking alone and waking from drunkenness and Robinson’s Miniver Cheevy, which ends by continuing to drink. Religious and literary treatments often frame drinking as a ritual, a vice, or a source of comic or tragic excess.
• Cannabis consumption
  • smoking marijuana — Smoking marijuana is the action celebrated in songs like The Toyes’ “Smoke Two Joints,” Snoop Dogg’s “Gin and Juice,” and Dr. Dre’s “The Next Episode.” It also appears as a Rastafarian ritual practice and as a shared activity in Raymond Carver’s fiction.
• Substance abuse epidemic
  • opioid crisis — The opioid crisis is the public-health epidemic of addiction, overdose, and deaths of despair linked in part to prescription painkillers and companies like Purdue Pharma. Clues may reference the Sackler family, OxyContin, and the work of Anne Case and Angus Deaton on related social decline.
    • Purdue Pharma — Purdue Pharma is the drug company owned by members of the Sackler family and best known for marketing OxyContin. It became a major symbol of the opioid epidemic and later pleaded guilty to misleading the public about the drug’s addictiveness.
• temperance and prohibition
  • Carrie Nation — Carrie Nation was a temperance and Prohibition activist famous for attacking saloons and bars with a hatchet in support of prohibition. She became notorious in Kansas for direct attacks on alcohol sellers and combative anti-liquor campaigning, and she was associated with the Woman’s Christian Temperance Union, including helping found a WCTU chapter in Kansas. She called her saloon-smashing campaigns “hatchetations” and promoted prohibition through speeches and publications such as Home Defender and the Smasher’s Mail. Her autobiography and public stunts made her one of the most recognizable Prohibition-era reformers.
• Drug prevention campaigns
  • Youth anti-drug campaigns
    • Above the Influence — Above the Influence was a National Youth Anti-Drug Media Campaign aimed at discouraging teen drug use. Its ads included the SLOMing concept and the initiative later continued under the Partnership to End Addiction.
• drug prevention programs
  • DARE or Drug Abuse Resistance Education — DARE, or Drug Abuse Resistance Education, is the school-based anti-drug program founded by Los Angeles police chief Darryl Gates in 1983. The clues emphasize its black T-shirts and later criticism that it did not reduce substance use.
• tobacco use
  • smoking — Smoking is the inhalation of burning tobacco, usually through cigarettes or other tobacco products. It is a major public-health target because it causes nicotine dependence and is strongly associated with lung cancer, cardiovascular disease, COPD, and many other health risks. Public-health campaigns, indoor smoking bans, cessation drugs, and programs ranging from motivational interviewing to medication such as bupropion have targeted it. Tobacco companies such as Philip Morris have been criticized for promoting smoking, and Turkmenistan’s Niyazov famously banned the habit after heart surgery. It has different effects on conditions such as Crohn’s disease and ulcerative colitis.
• Smoking and tobacco control

  • menthol cigarette — Menthol cigarettes are flavored tobacco products identified by their minty taste and cooling sensation. Quizbowl clues often connect them to targeted advertising toward Black consumers, debates over FDA restrictions, and brands like Kool, Uptown, and Decade.

  • non-smokers — These are people who do not smoke, especially those campaigning against second-hand smoke and indoor smoking restrictions. Clues point to advocacy efforts tied to public-health reporting, FCC cigarette commercials, and smoke-free laws such as Minnesota’s Freedom to Breathe Act.

  • Vaping — Vaping is the use of electronic cigarettes or similar devices to inhale aerosolized liquid. It has been the subject of flavor bans, youth-use controversies, and public health concern over products like Juul.

    • Juul — Juul is a major vaping company known for sleek pod-based e-cigarettes and flavored products. It became notorious for youth-oriented marketing controversies, nicotine dependence concerns, and regulatory crackdowns in the United States and Canada. The brand was later acquired by Altria Group.
• tobacco control
  • Luther Terry — Luther Terry was the U.S. Surgeon General who issued the first official government report linking smoking to health risks in 1964. That report helped drive mandatory cigarette warning labels and changed public discussion of tobacco use.

Nutrition and Infant Feeding

• Nutrition
  • baby formula — Baby formula is a manufactured milk substitute given to infants, especially when breastfeeding is not used or possible. Clues point to shortages and regulation of this product, including hospital access restrictions and the 2022 Abbott recall tied to bacterial contamination.
• nutrition and food security

  • starvation — Starvation is the state of severe food deprivation that can arise from deadlock in computing or from deliberate restriction of food intake. It is the condition central to Ancel Keys’s Minnesota Starvation Experiment and to Bret Harte’s The Outcasts of Poker Flat.

  • Supplemental Nutrition Assistance Program — The Supplemental Nutrition Assistance Program, or SNAP, is the modern food-stamp program in the United States. It grew out of Great Society anti-poverty policy and provides food aid to low-income Americans.

• Food insecurity
  • famine — A famine is a severe shortage of food that appears throughout scripture and history, from Joseph’s grain storage in Genesis to Agabus’s warning in Acts. The clues also point to disasters such as the Irish Famine, the Holodomor, and the Bengal famine of 1770. In Revelation, Famine is the black horseman who carries scales and announces the price of wheat. Tolstoy responded to the Russian famine of 1891-1892 with ‘A Terrible Question.’
    • famines — Famines are severe, catastrophic shortages of food that can result from crop failure, war, mismanagement, policy failure, or distribution and access problems rather than simple lack of food. Examples associated with them include the Holodomor, the Great Chinese Famine, the Irish Famine, the Bengal famine, and famines in the Sahel and the Horn of Africa. Amartya Sen is noted for arguing that famines often stem from inequality and entitlement problems.
• Infant feeding
  • breastfeeding — Breastfeeding is the act of feeding an infant milk from the breast, often discussed in public health, workplace policy, and campaigns against formula marketing. It appears in art as the Madonna lactans and in biology as a practice that can support infant nutrition when clean water is scarce.

Food Safety and Certification

• Animal disease scares
  • Mad cow disease
    • Howard Lyman — Howard Lyman is the vegetarian activist associated with Oprah Winfrey’s beef-defamation lawsuit after warning that U.S. cows could develop mad cow disease. He is identified in the clue by his appearance on Winfrey’s show and the resulting controversy.
• Food certification
  • Organic certification — Organic food certification refers to produce and other foods grown without synthetic chemicals. The USDA label also allowed some additives such as food colorings and gelatin under the 2007 rules mentioned here.
• food safety

  • Five-Second Rule — The five-second rule is the folk belief that dropped food is safe to eat if picked up quickly. It has been tested by studies on bacterial transfer to food from floors and other contaminated surfaces.

  • Jack in the Box — Jack in the Box is a fast-food chain known for its clown mascot, drive-through service, and the 1990s E. coli outbreak linked to contaminated meat. Its menu and ads often feature the character Jack, and the chain became a notable example of a major food-safety scandal.

Sanitation and Hygiene

• Sanitation
  • toilet — A toilet is the household plumbing fixture used for human waste disposal, often called a water closet in older terminology. Modern designs rely on a water seal to block odors, and the term became a common euphemism for the device.
• public hygiene
  • spitting — Spitting is the practice referenced by these clues, from folk rituals and legal customs to anti-spitting reform campaigns. The questions also point to the term’s older public-health and etiquette context, where cuspidors were common.
• Sanitary reform
  • Edwin Chadwick — Edwin Chadwick was a British sanitary reformer who argued for modernizing London’s sewers after the Great Stink. His 1842 report on urban poverty linked filthy sanitary conditions in London to contaminated water and disease.

Emergency and Injury Prevention

• Crowd disasters
  • crowd crush — A crowd crush is a disaster in which people are compressed, trampled, or suffocated in a dense mass of people. Famous examples include Hillsborough, the 1971 Ibrox disaster, the 2022 Itaewon tragedy, and the Astroworld concert deaths.
• Firefighting — Firefighting is the service of extinguishing blazes. It was historically performed by bucket brigades, insurance-company salvage corps, and the Roman vigiles. Historical accounts of organized firefighting mention Benjamin Franklin’s Union Fire Company, Crassus, and James Braidwood.
  • firefighter — This is the profession of firefighters, who answer fires and rescue work in cities from Edo to New York. Clues include hikeshi, Augustus’s vigiles, the Bowery Boys, the Vulcan Society, and the 9/11 first responders.
• Firefighting equipment
  • fire extinguisher — A fire extinguisher is a safety device used to smother flames, often by spraying out a chemical or powder. It becomes a darkly comic weapon or prop in films, games, and sports anecdotes because of the pressurized canister and nozzle.
• Personal protective equipment
  • eye protection
    • Safety goggles — Safety goggles are eye protection worn in labs to guard against chemical splashes and other hazards. They are a standard piece of personal protective equipment when mixing dangerous substances.
• protective equipment
  • Face masks — Face masks are protective coverings worn over the face in sports and ritual contexts. In the United States, they were widely used during the 1918 influenza pandemic and became a point of public controversy. Archaeological examples include elaborate mosaic masks at Teotihuacan and jade masks made by Olmec artisans; the term also covers football helmet face masks and the protective mask famously worn by Richard Hamilton.
• traffic safety
  • driving under the influence — Driving under the influence, also called driving while intoxicated or drunk driving, is operating a vehicle while alcohol-impaired. It is commonly prosecuted with breathalyzer evidence, is the act opposed by Mothers Against Drunk Driving (MADD), and is associated with designated drivers, ignition interlocks, and public safety campaigns against alcohol-impaired driving.

Environment and Social Conditions

Trace how environmental and social conditions influence population health.

Environmental and Occupational Health

• Exposure, Risk Assessment, and Prevention

  • Hazard and risk — a hazard can cause harm; risk combines the probability and consequence of harm under a specified exposure scenario.

  • Dose-response relationship — describes how outcome frequency or severity changes with exposure dose. Thresholds, latency, susceptible subgroups, and mixtures can complicate the relationship.

  • Exposure assessment — estimates contact with biological, chemical, physical, or social agents by route, intensity, frequency, and duration.

  • Source-pathway-receptor model — traces a hazard from its origin through environmental transport and an exposure route to an affected person or population, identifying points for control.

  • Cumulative exposure — combined exposure to multiple agents or repeated exposure over time. Mixtures, timing, vulnerability, and social conditions can matter beyond a single-agent dose.

  • Biomonitoring — measures chemicals, metabolites, or biological markers in human specimens. Detection establishes internal exposure but not automatically its source, timing, or health effect.

  • Risk characterization — integrates hazard, dose-response, exposure, and uncertainty into a decision-relevant account of expected harm and its limits.

  • Occupational hierarchy of controls — prioritizes elimination, substitution, engineering controls, administrative controls, and personal protective equipment, in that order.

  • Health impact assessment — prospectively evaluates how a policy, plan, or project could affect health distribution and recommends ways to enhance benefit and reduce harm.

  • Environmental epidemiology — studies health effects of physical, chemical, biological, and social environmental exposures using designs that must address spatial, temporal, and measurement uncertainty.

• Places, Pollution, and Environmental Emergencies

  • Built environment — housing, land use, transportation, public space, and infrastructure shape injury, physical activity, heat, pollution, access, and social connection.

  • Environmental justice — examines unequal environmental burdens, benefits, participation, and enforcement, especially where structural disadvantage shapes exposure and vulnerability. It is often described as a movement arguing that environmental harms and policy costs fall disproportionately on minority communities, and it is linked to the ideas of environmental racism and environmental equity.

  • Climate and health — climate change influences heat illness, air quality, infectious-disease ecology, food and water security, disasters, displacement, and mental health, with unequal vulnerability.

  • environmental pollution
    • air pollution — Air pollution is the buildup of harmful particulates and gases such as NOx, SOx, and ozone in the atmosphere. Clues often mention PM2.5, the AQI, London smog, wildfire smoke, or laws such as the Clean Air Act.

      • Particulate matter — Particulate matter is a pollution term for tiny solid or liquid particles suspended in air. It appears in standards such as PM10 and is often discussed in connection with burn pit smoke and asthma-causing fine matter.

      • Particulate matter 10 microns in size — PM10 is particulate matter made up of particles 10 microns or smaller in diameter. It is one of the classic criteria pollutants used in U.S. air-quality regulation.

    • noise pollution — Noise pollution is harmful pollution caused by elevated sound levels. It is associated with complaints about loud neighborhood and industrial noise, including the kind produced by traffic and carpet-beating.
  • environmental health

    • drinking water — Drinking water is water safe for human consumption, and the clues focus on testing, contamination, and public access to that resource. It comes up in discussions of coliform bacteria, Flint’s lead crisis, and unequal access in colonia communities.

    • drinking water safety
      • Safe Drinking Water Act — The Safe Drinking Water Act is the 1974 U.S. law that lets the EPA regulate contaminants in public drinking water. It is especially associated with oversight of pathogens such as Cryptosporidium, Giardia, and Legionella.
    • plastic pollution
      • plastic bags — Plastic bags are single-use polyethylene carryout bags widely targeted by anti-pollution bans. Pacific island nations, Bangladesh, Rwanda, and Hawaii all appear in examples of restrictions on these items.
    • Silent Spring — Silent Spring is Rachel Carson’s 1962 environmental classic warning that pesticides such as DDT can devastate ecosystems and kill birds. Its opening fable imagines a town silenced by a strange blight, and the book helped trigger major criticism of pesticide use and a broader environmental movement.
  • water, sanitation, and hygiene
    • diarrhea — Diarrhea is the condition of frequent loose bowel movements, often caused by infections such as rotavirus, cholera, or C. difficile. It is also the public-health focus of WASH programs and can be referred to in broader terms when bloody or dysenteric symptoms are emphasized.
  • environmental treaties
    • Montreal Protocol — The Montreal Protocol is the 1987-1989 ozone treaty that phased out CFCs and HCFCs. It created financial mechanisms such as the Multilateral Fund and became the first treaty to achieve universal ratification.
  • industrial disasters

    • Bhopal — Bhopal is the Indian city remembered for the 1984 Union Carbide gas leak that released methyl isocyanate. The disaster is widely treated as the deadliest industrial accident in history.

    • Chemical disasters

      • Bhopal disaster — The Bhopal disaster was the 1984 Union Carbide gas leak in Madhya Pradesh, where methyl isocyanate killed thousands and left long-term health damage.
  • Radiation accidents
    • Goiania — Goiânia, Brazil was the site of a major cesium-137 contamination incident after a discarded medical source was dismantled in a junkyard. The radiation leak sickened residents and became one of the most serious radioactive accidents outside Chernobyl.
  • sun protection
    • Sun Protection Factor — Sun protection factor, or SPF, is the rating used for sunscreens. It measures how much UV radiation is blocked and how much longer protected skin can remain in the sun compared with unprotected skin.

Social Determinants of Health

• social isolation — Social isolation is the condition of being cut off from regular contact with other people, and it is often linked with loneliness and emotional isolation. It has been studied as a public health issue through measures such as the UCLA loneliness scale and by work connecting it to mortality and cognitive decline.

Health Systems, Ethics, and Organizations

Compare health systems and organizations through their functions and responsibilities.

Health Systems, Policy, and Ethics

• Health Systems, Financing, and Access

  • Health system — the people, institutions, financing, information, products, and governance involved in maintaining or improving health. Clinical care is one component of a broader system.

  • healthcare — Healthcare is the policy area dealing with medical services, insurance, and public health systems such as single-payer or the National Health Service. Debates over U.S. reform often center on mandates, cost sharing, and the Affordable Care Act.

  • health care systems

    • universal health care — Universal health care is a system in which medical treatment is financed so that everyone can receive care, often through taxes or public insurance. Clues include the British NHS, the Beveridge report’s language of freedom from want, and American debates over Massachusetts-style mandates.

    • Single-payer health care

      • Canadian Health Care system — The Canadian health care system is the country’s publicly funded single-payer medical system, commonly called medicare. It was developed through provincial and federal reforms associated with Tommy Douglas and later expanded under the Canada Health Act.

  • Primary care — first-contact, accessible, continuous, comprehensive, and coordinated care. It differs from primary prevention, which describes timing of preventive action.

  • Universal health coverage — access to needed quality services without financial hardship. Coverage on paper does not guarantee timely, acceptable, or effective care.

  • Health insurance risk pooling — combines financial risk across people so unpredictable individual costs are shared. Pool size, selection, benefits, prices, and subsidies affect protection.

  • Medicaid — Medicaid is the U.S. public health insurance program for low-income people, funded jointly by the federal government and the states. It was expanded under the Affordable Care Act and became a major issue in NFIB v. Sebelius, which blocked federal threats to withhold its funding from noncomplying states.

  • Medicare
    • Medicare Advantage — Medicare Advantage, also called Medicare Part C, is the Medicare program in which private insurers provide coverage to enrollees. It is widely used by seniors and is often discussed in debates over costs and access to urgent care.

  • Access to care — the practical ability to obtain appropriate services when needed. Availability, affordability, geography, language, trust, disability access, and administrative burden all contribute.

  • Health-care utilization — use of services such as preventive, outpatient, emergency, inpatient, pharmacy, and long-term care. Higher use can indicate either better access or greater unmet health need.

  • Continuity of care — coherent care over time across clinicians and settings through stable relationships, shared information, coordinated plans, and reliable transitions.
• Quality, Evidence, and Allocation

  • Quality of care — commonly includes safety, effectiveness, patient-centeredness, timeliness, efficiency, and equity. Measurement can create incentives and must be checked for gaming and case-mix differences.

  • Cost-effectiveness analysis — compares incremental costs and health consequences across options. It informs efficiency but does not by itself decide distribution, affordability, rights, or political feasibility.

  • Health technology assessment — evaluates clinical effects, safety, cost, ethics, organizational consequences, and social implications of a health technology for a defined policy decision.

  • Priority setting — allocates limited resources among competing health needs using evidence, values, opportunity costs, equity, transparency, and appeal or revision processes.

  • evidence-based medicine

    • Cochrane collaboration — The Cochrane Collaboration is a British organization known for systematic reviews and plain-language summaries of medical evidence. Its reviews are widely treated as high-quality evidence in clinical practice.
• Ethics, Participation, and Historical Abuses

  • Public-health ethics — balances population benefit, individual liberty, justice, reciprocity, transparency, proportionality, and the least restrictive effective means.

  • Community engagement — includes affected communities in setting priorities, designing interventions, interpreting evidence, and sharing authority. Consultation without influence is not meaningful participation.

  • Data privacy — limits collection, access, linkage, use, retention, and disclosure of identifiable information. De-identification reduces but may not eliminate re-identification risk.

  • Ethics scandals
    • Tuskegee syphilis study — A notorious U.S. Public Health Service study in Macon County, Alabama, in which Black sharecroppers with syphilis were left untreated so doctors could observe the course of the disease. It involved hundreds of Black men, was backed early on by the Rosenwald Fund, was exposed by Jean Heller and Peter Buxtun, later became infamous for its extension to Guatemala, and became a classic bioethics scandal that helped prompt the Belmont Report.
  • Medical ethics and experimentation
    • Tuskegee — Tuskegee is the Alabama city and university associated with the notorious syphilis study on Black men and with the Tuskegee Airmen. The study became a byword for unethical medical experimentation and helped spur modern informed-consent rules.
  • euthanasia and assisted suicide
    • Final Exit — Final Exit is Derek Humphry’s controversial book about assisted suicide and self-deliverance for the terminally ill. It became closely associated with the Hemlock Society and drew public attention to suicide methods.
• Institutions, Advocacy, and Population Policies
  • Public health offices
    • Surgeon General of the United States — The Surgeon General of the United States heads the U.S. Public Health Service Commissioned Corps. The office became widely associated with public health warnings, especially the landmark cigarette-health advisory issued during Luther Terry’s tenure.
  • Public health policy
    • mask mandates — Mask mandates are public-health rules requiring face coverings to slow the spread of COVID-19. They became a major political flashpoint during debates over school policy, state executive orders, and pandemic restrictions.
  • health policy
    • universal single-payer healthcare — Universal single-payer healthcare is a system in which the government collects taxes to pay medical costs for all residents. It replaces most private insurance by having a single public payer cover healthcare services for everyone.
  • Health agencies

    • Centers for Disease Control and Prevention — The Centers for Disease Control and Prevention is the Atlanta-based U.S. public health agency that publishes the Morbidity and Mortality Weekly Report, issues travel health notices, collects health statistics, and handles surveillance and data reporting on topics such as gun violence and overdose trends. It became especially prominent during COVID-19, when it was led by Rochelle Walensky and recommended masking. The agency was formerly called the Communicable Disease Center.

    • National Institutes of Health — The National Institutes of Health is the U.S. biomedical research agency in Bethesda that funds medical studies and runs the Clinical Center and National Library of Medicine. It is organized into multiple institutes and centers within the Department of Health and Human Services.

  • global health
    • Mountains Beyond Mountains — Mountains Beyond Mountains is Tracy Kidder’s biography of Paul Farmer and his global health work. The book follows Farmer’s efforts to fight tuberculosis and to bring antibiotics and care to places such as Haiti and Peru.
  • reproductive health

    • female genital mutilation — Female genital mutilation is a harmful practice that includes infibulation and clitoridectomy and has been the target of international abolition campaigns. The clues point to work by activists such as Stella Obasanjo and Efua Dorkenoo, along with criticism in literature and film.

    • Planned Parenthood — Planned Parenthood is the American reproductive-health organization founded by Margaret Sanger and often targeted in political controversies over abortion. It appears in clues about funding fights, undercover filming, and state lawsuits over access to reproductive services.

    • The Woman Rebel — The Woman Rebel was Margaret Sanger’s radical birth-control newsletter, the publication that brought obscenity trouble and helped define her early activism. It is tied to her campaign for reproductive rights, anti-Comstock agitation, and the writings that made her a central figure in the birth-control movement.

  • women’s health
    • tampons — Tampons are absorbent feminine hygiene products designed for internal use during menstruation. They became associated with toxic shock syndrome after highly absorbent versions were linked to the illness.
  • Population policy
    • population control — Population control refers to policies meant to reduce birth rates or slow population growth. It is associated with family planning campaigns, the One Child Policy, and debates over coercion, development, and demographic imbalance.
  • reproductive health organizations
    • Planned Parenthood Federation of America — Planned Parenthood Federation of America is a U.S. reproductive health organization founded by Margaret Sanger. It provides contraception and abortion services and has been central to debates over abortion access, federal funding, and clinic attacks. It is associated with major Supreme Court cases including Roe v. Wade and Planned Parenthood v. Casey, and with the Hyde Amendment.
  • contraception

    • Condoms — Condoms are barrier contraceptives whose advertising has often been controversial, but they became more visible in anti-AIDS public health campaigns.

    • birth control — The prevention of pregnancy by devices, drugs, or other methods, including condoms, other barrier methods, and hormonal pills. Historical examples include herbal or mechanical barriers, ancient pessaries, and silphium. It has been the subject of religious, medical, and legal controversy, including the Comstock laws and Catholic objections to artificial family planning.

  • sexual health education
    • Joycelyn Elders — Joycelyn Elders was Bill Clinton’s Surgeon General and a controversial public-health advocate. She drew criticism for supporting sex education, condom access, and frank discussions of masturbation as part of AIDS prevention.
  • blood donation
    • donating blood — Donating blood is the act described by the clues, including references to bans on certain donors and shortages caused by restrictions on reciprocal blood donation. It is a common public-health topic tied to eligibility rules and blood supply policy.
  • AIDS activism and policy

    • ACT UP — ACT UP is the direct-action AIDS activist group associated with the slogan “Silence = Death.” The name stands for AIDS Coalition to Unleash Power. Founded in the wake of Larry Kramer’s 1987 speech, it became known for disruptive protests demanding better treatment and prevention policy.

    • Ryan White — Ryan White was the Indiana teenager with hemophilia who became a public symbol of the AIDS crisis after contracting HIV from a blood transfusion. The federal Ryan White CARE Act is named for him and funded AIDS treatment and support services.

    • Scott H. Evertz — Scott H. Evertz was an openly gay appointee who headed the White House Office of National AIDS Policy under George W. Bush. His appointment drew attention because it cut across expected partisan lines on AIDS policy and gay representation.

  • HIV/AIDS relief programs
    • PEPFAR — PEPFAR is the U.S. President’s Emergency Plan for AIDS Relief, launched in 2003 as a major anti-HIV program. It has been credited with saving millions of lives, and Anthony Fauci received the Medal of Freedom for work connected to its development.

  • tobacco industry — The tobacco industry is the target of landmark anti-smoking campaigns, lawsuits, and public-health investigations. Clues often reference Philip Morris, the Marlboro Man, the Master Settlement Agreement, or whistleblowers and documentaries such as The Insider.

  • vaccine controversies
    • Andrew Wakefield — Andrew Wakefield is the disgraced physician whose fraudulent 1998 paper in The Lancet falsely linked the MMR vaccine to autism. The paper was later retracted, and his claims helped spread modern anti-vaccine conspiracy theories.
  • humanitarian medicine
    • Henry Dunant — Swiss humanitarian best known for A Memory of Solferino, his vivid account of battlefield suffering after the battle of Solferino. He urged the creation of neutral relief societies for the wounded, helped inspire the International Committee of the Red Cross, and was honored with the first Nobel Peace Prize in 1901 alongside Frederic Passy for humanitarian work that helped transform wartime medical aid.

Humanitarian Aid Organizations

• Humanitarian organizations
  • American Red Cross — The American Red Cross is the humanitarian organization founded by Clara Barton to provide disaster relief, first aid, and wartime medical support. Its early history includes Barton’s Office of Missing Soldiers and major responses such as the Johnstown Flood.
    • Clara Barton — Clara Barton was a Civil War nurse nicknamed the “Angel of the Battlefield” who later founded the American Red Cross. She also organized the Office of Missing Soldiers and became known for disaster relief work, including after the Johnstown Flood.
  • International Movement of the Red Cross and Red Crescent — The International Movement of the Red Cross and Red Crescent grew out of Henri Dunant’s response to the Battle of Solferino in 1859. It is headquartered in Geneva and is a multiple-time Nobel Peace Prize recipient.
• International Red Cross and Red Crescent Movement
  • International Committee of the Red Cross — The International Committee of the Red Cross was founded in Geneva in response to Henri Dunant’s account of Solferino and became the core international humanitarian organization for care of wounded soldiers. Clues often mention Clara Barton’s American branch and the Swiss-flag-inspired red cross emblem.
• Medical humanitarian NGOs
  • Doctors Without Borders — Doctors Without Borders, or Médecins Sans Frontières, is the international medical NGO founded during the Biafran War by French doctors including Bernard Kouchner. It won the 1999 Nobel Peace Prize and is known for work in conflict zones and refugee crises.
• Red Cross and Red Crescent
  • Red Crescent — The Red Crescent is the humanitarian emblem used in many Muslim-majority countries as an alternative to the Red Cross. It marks medical and relief personnel and is shaped like a crescent moon.

Health Charities and Advocacy

• Cancer charities

  • Livestrong — Livestrong is the cancer-awareness brand associated with the yellow wristbands promoted by Lance Armstrong and his foundation. The name is especially tied to fundraising and public support for cancer research.

  • Susan G. Komen for the Cure — Susan G. Komen for the Cure is a breast cancer charity founded by Nancy Brinker and named for her sister Susan G. Komen. It is known for Race for the Cure fundraising and for controversy over its ties to Planned Parenthood and pink-ribbon marketing.

• cardiovascular health
  • American Heart Association — The American Heart Association is a Dallas-based health organization founded in 1924 that publishes Circulation and supports research on cardiovascular disease. It also certifies foods with its red-check mark and offers CPR training, including the Heartsaver program.
• Children’s health charities
  • March of Dimes — The March of Dimes is an American charity founded by Franklin D. Roosevelt to fight polio. It began as the National Foundation for Infantile Paralysis and later shifted toward work on premature birth and birth defects.

Sources and Further Study

Use the sources to deepen questions raised by the preceding chapters.

• CDC, Principles of Epidemiology in Public Health Practice

• CDC, Introduction to Epidemiology

• CDC, Field Epidemiology Manual

• World Health Organization, health topics

• Hernán and Robins, Causal Inference: What If