Public Health & Preventive Medicine

01 Defining Public Health

Public health is the science and art of preventing disease, prolonging life, and promoting health through the organized efforts of society. Coined by C.-E. A. Winslow in 1920, this definition still anchors the field: unlike clinical medicine, which treats individuals one at a time, public health focuses on populations, upstream determinants, and systems-level interventions. The unit of analysis is the community — a neighborhood, a workforce, a city, a nation, or the entire globe.

Public Health vs. Clinical Medicine

Levels of Prevention

Primordial prevention targets the underlying social and environmental conditions that create risk factors (e.g., urban planning that enables walking). Primary prevention prevents disease onset (vaccination, tobacco taxes, fluoridation). Secondary prevention detects disease early when intervention is effective (mammography, HTN screening). Tertiary prevention reduces complications and disability in established disease (cardiac rehab, diabetes self-management). Quaternary prevention protects patients from unnecessary medical interventions (overdiagnosis, overtreatment).

The Determinants of Health

Health outcomes are shaped by a mix of factors, often summarized as: genetics and biology (~10%), health behaviors (~30%), medical care (~10–20%), social and economic factors (~40%), and physical environment (~10%). These County Health Rankings weights are approximate but conceptually central: most of what determines whether a person is healthy happens outside the clinic.

Population vs High-Risk Strategies

Geoffrey Rose distinguished two approaches to prevention. The high-risk strategy targets individuals at highest risk (e.g., statins for those with 10-year ASCVD ≥ 10%). The population strategy shifts the distribution of risk in the whole population (e.g., reducing dietary sodium, cigarette taxes). Rose's paradox: "A large number of people at small risk may give rise to more cases of disease than a small number at high risk." Most public health gains come from population strategies because risk is rarely bimodal — the tail of the distribution is fat.

02 Core Functions & Essential Services

In 1988, the Institute of Medicine's landmark report The Future of Public Health defined three core functions: assessment (monitor health, diagnose problems), policy development (inform, educate, mobilize partnerships, develop policies), and assurance (enforce laws, link people to services, ensure a competent workforce, evaluate). These functions are operationalized through the Ten Essential Public Health Services, updated in 2020 to place equity at the center.

The Ten Essential Public Health Services (2020 Framework)

The Public Health Pyramid (Frieden, 2010)

Thomas Frieden's Health Impact Pyramid ranks interventions by the scale of benefit and the effort required by individuals. Socioeconomic factors (bottom) have the largest impact; counseling (top) the smallest. Effective public health invests heavily in the base.

Ten Great Public Health Achievements (20th Century, CDC)

• Vaccination — eliminated/controlled measles, polio, diphtheria, rubella in the US
• Motor vehicle safety — seat belts, child safety seats, airbags, graduated licensing
• Safer workplaces — OSHA, hazard controls, ergonomics
• Control of infectious diseases — sanitation, clean water, antimicrobials
• Decline in CHD and stroke deaths — smoking control, BP/cholesterol management, reperfusion
• Safer and healthier foods — fortification, refrigeration, inspection
• Healthier mothers and babies — prenatal care, neonatal intensive care, folic acid
• Family planning — contraception access, maternal mortality reductions
• Fluoridation of drinking water — 25% reductions in tooth decay at all ages
• Recognition of tobacco as a health hazard — since 1964 Surgeon General report

03 History of Public Health

Public health began as sanitation. Ancient Rome built aqueducts and sewers; medieval quarantines ("quaranta giorni" — forty days) isolated ships arriving in Venice during the Black Death. The modern era began in 19th-century Europe, where industrialization crowded workers into unsanitary cities and the germ theory replaced miasma.

Landmark Figures & Events

04 Public Health Agencies & Infrastructure

US public health is fragmented across federal, state, and local levels. The federal role is primarily funding, standard-setting, and surveillance; states hold constitutional police power over health; local health departments deliver most frontline services.

Major Federal Agencies

Federal Funding Mechanisms

Global & International

The World Health Organization (WHO) coordinates international health, sets norms (International Health Regulations 2005), maintains the ICD, and declares Public Health Emergencies of International Concern (PHEIC). Regional offices (PAHO for the Americas, EURO, AFRO, SEARO, EMRO, WPRO) carry out regional work. Other key actors include UNICEF (child health, cold chain), Gavi (vaccine procurement for low-income countries), the Global Fund (HIV, TB, malaria), and PEPFAR (US HIV/AIDS program).

Local Health Departments

The US has roughly 3,000 local health departments (LHDs), varying enormously in size, governance, and scope. Larger urban departments (NYC DOHMH, LA County, Chicago) function as peers to state agencies; many rural LHDs serve tiny populations with skeletal staff. Typical LHD functions include communicable disease investigation, immunizations, WIC, STI clinics, restaurant inspections, vital records, tobacco control, tuberculosis treatment, emergency preparedness, and maternal-child health services. The Public Health Accreditation Board (PHAB) offers voluntary accreditation.

Public Health Workforce

The US public health workforce is chronically understaffed — state and local health departments lost roughly a fifth of their workforce between 2008 and 2019, then faced a massive COVID-19 surge. Core roles include epidemiologists, environmental health specialists, public health nurses, health educators, disease intervention specialists, community health workers, biostatisticians, and public health physicians. The CDC's Epidemic Intelligence Service (EIS) is the flagship training program for field epidemiologists (the "disease detectives").

05 Descriptive & Analytic Epidemiology

Epidemiology is the basic science of public health: the study of the distribution (descriptive) and determinants (analytic) of health-related states in populations. While biostatistics provides the quantitative tools, epidemiology asks the questions.

Descriptive Epidemiology — Person, Place, Time

Descriptive studies characterize who is affected (age, sex, race, occupation), where (geographic distribution, urban vs rural), and when (seasonal, secular trends, clustering). Descriptive work generates hypotheses that analytic studies then test.

Measures of Association vs Impact

Epidemiologic measures fall into two groups. Measures of association (relative risk, odds ratio, hazard ratio) describe the strength of the exposure-outcome relationship and are used for etiologic inference. Measures of impact (attributable risk, population attributable fraction, number needed to treat) describe the burden that could be averted by removing the exposure and are used for public health decision-making. A rare exposure with a large RR may have a small population impact; a common exposure with a small RR may have a large population impact.

Analytic Study Designs

Key Measures

Incidence = new cases / person-time at risk (dynamic flow). Prevalence = total cases / population at a point in time (stock). Prevalence ≈ Incidence × Duration. Attack rate = ill / exposed during an outbreak (a special case of incidence). Case fatality rate = deaths / cases. Mortality rate = deaths / population. Years of potential life lost (YPLL) weights premature deaths more heavily. DALYs (disability-adjusted life years) combine mortality and morbidity for global burden comparisons.

Causal Inference — Bradford Hill Considerations

Austin Bradford Hill's 1965 criteria help judge whether an observed association is likely causal. They are guides, not requirements:

• Strength — larger effects are harder to explain by bias/confounding
• Consistency — replicated in different populations, places, times
• Specificity — one cause, one effect (rarely met in practice)
• Temporality — cause precedes effect (the only non-negotiable criterion)
• Biological gradient — dose-response relationship
• Plausibility — biologically reasonable mechanism
• Coherence — fits existing knowledge
• Experiment — intervention removes the exposure and outcome decreases
• Analogy — similar exposures produce similar outcomes

These were marshaled in the 1964 Surgeon General's report on smoking and remain central to environmental epidemiology and tort litigation.

06 Surveillance Systems

Surveillance is the ongoing, systematic collection, analysis, and interpretation of health data for action. "Data for action" is the operative phrase — surveillance that doesn't drive intervention is just statistics.

Types of Surveillance

Key US Surveillance Systems

NNDSS (National Notifiable Diseases Surveillance System) aggregates state reports weekly via MMWR. BRFSS is the largest ongoing telephone health survey (behavioral risk factors, state-level). NHANES combines interviews with physical exams and labs on a nationally representative sample. YRBSS surveys high school students. NVSS tracks births and deaths via vital records. NHSN tracks healthcare-associated infections.

07 Outbreak Investigation

The CDC outlines a standard 10-step outbreak investigation that field epidemiologists (EIS officers) follow. Steps may be performed iteratively or in parallel, not strictly sequentially.

Epidemic vs Outbreak vs Cluster

Terminology is imprecise but carries connotation. An outbreak is typically a localized rise in disease, while an epidemic often implies a broader geographic reach or political weight — the two are scientifically synonymous. A cluster is an aggregation without yet demonstrating excess over baseline. A pandemic is a worldwide epidemic. Declaring an epidemic can have legal, economic, and political consequences — officials sometimes avoid the word even when it is accurate.

The Ten Steps

Epidemic Curves

The epi curve plots case counts by date of onset. Its shape suggests the propagation pattern: point source (single sharp peak, all cases within one incubation period — e.g., a contaminated meal), continuous common source (plateau, ongoing exposure), propagated (successive peaks one incubation period apart — person-to-person spread), and mixed.

Reed-Frost Model

The Reed-Frost model is a simple deterministic epidemic model describing a closed population of susceptibles (S), cases (C), and immunes. Given a probability p that a susceptible contacts an infectious case during the infectious period, C_t+1 = S_t(1 − (1 − p)^Ct). It illustrates how herd immunity and attack rate emerge from contact structure.

Case Definition & Line List

A case definition specifies clinical, laboratory, and epidemiologic criteria for counting someone as a case. Definitions are typically tiered as confirmed (lab confirmation required), probable (clinical criteria + epi link), and suspect (clinical only). Case definitions should be sensitive early in an investigation (to avoid missing cases) and tightened later once the etiology is known.

A line list is the foundational dataset of an outbreak — one row per case, columns for demographics, date of onset, symptoms, exposures, lab results, and outcomes. Even in the era of sophisticated databases, epidemiologists still start investigations with a line list on a spreadsheet.

Cluster Investigation

A cluster is a real or perceived aggregation of health events grouped in time and/or place. Classic examples include cancer clusters and reproductive outcome clusters. Most suspected clusters, when investigated, turn out to be statistical noise or recall bias — true environmental clusters with identifiable exposures are rare. The CDC's 2013 guidelines emphasize rigorous assessment, community engagement, and transparent communication regardless of outcome.

08 Reportable & Notifiable Diseases

Each US state defines its own reportable disease list (clinicians and labs must report to the state); states then voluntarily report to CDC's nationally notifiable list. As of recent CDC updates, roughly 120 conditions are nationally notifiable.

Mandatory Reporting by Clinicians

Beyond reportable diseases, clinicians have mandatory reporting obligations including: suspected child abuse or neglect, elder abuse (most states), gunshot and stab wounds (most states), animal bites for rabies surveillance, certain occupational diseases, some injuries related to impairment while driving, and deaths in specific circumstances (coroner cases). Mandatory reporting laws generally provide civil and criminal immunity for good-faith reports.

Select Nationally Notifiable Conditions

09 Chain of Infection & Transmission

The chain of infection describes the six links required to sustain transmission. Breaking any single link interrupts the chain — this is the conceptual basis for every infection control intervention.

The Six Links

Modes of Transmission

Direct contact — physical transfer (STIs, scabies, impetigo). Indirect contact — via fomites (norovirus, MRSA). Droplet — large respiratory droplets (> 5 μm) traveling < 6 feet (influenza, pertussis, meningococcus, SARS-CoV-2 — primarily). Airborne — droplet nuclei (< 5 μm) suspended and inhaled at a distance (TB, measles, varicella). Vehicle — food, water, blood products. Vector-borne — arthropod (mosquito, tick, flea).

Hospital Transmission-Based Precautions (CDC)

Incubation & Infectious Periods

10 Herd Immunity & R₀

Herd immunity (community immunity) is the indirect protection of susceptible individuals that occurs when a sufficiently large proportion of the population is immune, so that transmission cannot sustain itself. It is the mathematical reason vaccines protect even those who cannot be vaccinated (infants, immunocompromised).

R₀ and the Herd Immunity Threshold

Basic reproduction number (R₀) is the average number of secondary cases produced by one infectious case in a fully susceptible population. Effective reproduction number (R_t or R_e) is the real-time value accounting for immunity and interventions. When R_t < 1, the epidemic shrinks.

The herd immunity threshold (HIT) is the proportion that must be immune to drive R_t < 1: HIT = 1 − 1/R₀.

R₀ of Selected Pathogens

Limitations of the HIT Concept

The herd immunity threshold assumes homogeneous mixing, lifelong sterilizing immunity, and a closed population — assumptions rarely fully met in practice. In reality, (1) contact networks are clustered, so local pockets of susceptibility can sustain outbreaks even with high overall coverage; (2) vaccine-induced immunity wanes, and natural immunity may or may not be lifelong; (3) variants alter R₀; (4) not every vaccine prevents transmission equally well. COVID-19 made these caveats famous: vaccines that reduced severe disease did less to interrupt transmission than initially hoped.

11 Isolation, Quarantine & Contact Tracing

Isolation separates people who are ill with a contagious disease. Quarantine restricts the movement of asymptomatic people who have been exposed. Both are coercive tools with a long history in US law (Jacobson v. Massachusetts, 1905; federal authority at ports of entry under 42 USC §264).

Contact Tracing

Contact tracing identifies, notifies, and monitors individuals exposed to an infectious case. The steps are: (1) interview the index case to identify contacts during the infectious period; (2) notify contacts of exposure without disclosing the index case's identity; (3) assess and manage contacts — offer testing, post-exposure prophylaxis, quarantine; (4) monitor for symptoms through the incubation period.

Non-Pharmaceutical Interventions (NPIs)

12 HAI, AMR, TB, HIV/STI & Pandemic Preparedness

Healthcare-Associated Infections (HAI)

HAIs affect roughly 1 in 31 hospitalized patients. Major categories include central line-associated bloodstream infection (CLABSI), catheter-associated UTI (CAUTI), surgical site infection (SSI), ventilator-associated pneumonia (VAP), and C. difficile infection. The CDC's National Healthcare Safety Network (NHSN) is the primary reporting system; CMS reduces payment for excess HAIs under the Hospital-Acquired Condition Reduction Program.

Antimicrobial Resistance (AMR)

The CDC estimates > 2.8 million AMR infections and 35,000 deaths yearly in the US. Priority threats include C. difficile, carbapenem-resistant Enterobacterales (CRE), drug-resistant Neisseria gonorrhoeae, Candida auris, MRSA, ESBL producers, and multidrug-resistant TB. Core strategies: antimicrobial stewardship, infection prevention, surveillance, rapid diagnostics, and new drug development.

Hand Hygiene & Environmental Cleaning

Hand hygiene remains the single most important intervention to prevent HAI. WHO's "Five Moments for Hand Hygiene": before patient contact, before aseptic task, after body fluid exposure risk, after patient contact, after contact with patient surroundings. Alcohol-based handrub (60–95%) is preferred except when hands are visibly soiled or with spore-forming organisms (C. difficile, anthrax), when soap and water are required. Environmental cleaning with appropriate disinfectants, bundles for central lines and urinary catheters, ventilator bundles, and surgical checklists collectively have driven large HAI reductions.

Tuberculosis Control

TB control rests on: (1) finding and treating active disease (DOT — directly observed therapy), (2) identifying and treating latent TB infection (LTBI), (3) contact investigation, (4) infection control in healthcare and congregate settings, and (5) managing drug-resistant TB. First-line therapy: RIPE (rifampin, isoniazid, pyrazinamide, ethambutol) for 2 months, then RI for 4 months.

HIV & STI Prevention

Modern HIV prevention includes universal screening (opt-out) for ages 13–64, pre-exposure prophylaxis (PrEP), post-exposure prophylaxis (PEP), treatment as prevention (U=U: undetectable = untransmittable), condom distribution, syringe services programs, and perinatal HIV elimination. STI rates (chlamydia, gonorrhea, syphilis) have been rising; congenital syphilis resurged in the 2020s. Expedited partner therapy is legal in most states.

COVID-19 Pharmacologic & Non-Pharmacologic Interventions

Pandemic Preparedness & COVID-19 Lessons

13 Vaccine Types & Technology

Vaccines expose the immune system to antigens derived from a pathogen, producing immunologic memory without causing disease. Platform choice determines immunogenicity, safety profile, cold chain, and contraindications.

Vaccine Platforms

14 ACIP Schedules & Catch-Up

The Advisory Committee on Immunization Practices (ACIP) develops US civilian immunization recommendations. Once CDC Director approves, recommendations are published in the MMWR, incorporated into the Vaccines for Children (VFC) program, and required to be covered without cost-sharing by ACA-compliant insurance.

Recommendations are developed through systematic literature review by ACIP workgroups, presented for public comment, voted on by the full committee in public meetings, and finalized when signed by the CDC director. Implementation is supported by clinical materials, provider education, and the VFC program for eligible children.

Childhood Schedule (High-Yield Summary)

Vaccines for Children (VFC) Program

Established after the 1989–1991 measles resurgence, the VFC program provides free vaccines to children who are Medicaid-eligible, uninsured, underinsured, or American Indian / Alaska Native. Vaccines are purchased federally at reduced cost and distributed through enrolled providers. VFC has been credited with substantially reducing disparities in childhood vaccination rates.

Adult Schedule Highlights

Catch-Up Vaccination Principles

Children more than one month behind follow CDC catch-up schedules. Core principles: (1) do not restart a series — count every valid dose; (2) observe minimum intervals between doses; (3) minimum ages must be met; (4) give all due vaccines at the same visit; (5) simultaneous administration is safe and maximizes opportunity; (6) do not delay for mild illness or antibiotic use; (7) pre-vaccination serology is rarely necessary.

School & Immunization Mandates

All US states require specified vaccines for school entry. All 50 states allow medical exemptions; most allow religious exemptions; roughly 15 states allow philosophical exemptions. Tighter exemption policies correlate with higher coverage and fewer outbreaks — California's SB277 (2015), eliminating non-medical exemptions after a Disneyland measles outbreak, is the most-studied example. Immunization Information Systems (registries) consolidate records across providers and support reminder/recall.

15 Contraindications, Hesitancy & Safety Monitoring

Contraindications & Precautions

Vaccine Hesitancy

WHO listed vaccine hesitancy as one of the top 10 global health threats in 2019. Drivers include the 3 Cs: confidence (trust in vaccines and providers), complacency (perceived low disease risk), and convenience (access). The retracted 1998 Wakefield paper falsely linking MMR to autism fueled decades of misinformation. Effective responses: presumptive recommendation, motivational interviewing, trusted community messengers, and countering misinformation early.

Safety Monitoring Systems

16 USPSTF & Screening Principles

The US Preventive Services Task Force (USPSTF) is an independent volunteer panel of national experts in prevention and evidence-based medicine that makes recommendations about clinical preventive services. ACA Section 2713 requires that A- and B-graded services be covered without cost-sharing by private insurance and Medicare.

Sources of Prevention Recommendations

USPSTF Grades

Wilson & Jungner Screening Criteria (1968)

A screening program should satisfy classic Wilson & Jungner criteria: (1) the condition should be an important health problem; (2) there should be an accepted treatment; (3) facilities for diagnosis and treatment should be available; (4) there should be a recognizable latent or early symptomatic stage; (5) there should be a suitable test; (6) the test should be acceptable to the population; (7) the natural history should be adequately understood; (8) there should be an agreed policy on whom to treat; (9) the cost should be economically balanced; (10) case-finding should be a continuing process.

Biases in Screening Evaluation

Lead-time bias — screening appears to prolong survival by moving the diagnosis date earlier, even if it doesn't change the time of death. Length-time bias — screening preferentially detects slowly progressive (less aggressive) cases, making screened cohorts look like they do better. Overdiagnosis — detection of disease that would never have caused harm in the patient's lifetime (a form of length-time bias at its extreme). Selection bias — people who attend screening are healthier than those who don't.

Criteria for a Good Screening Test

Beyond the Wilson-Jungner condition-level criteria, the screening test itself should be simple and inexpensive, safe, acceptable to the population, reliable (reproducible), valid (sensitive and specific), and have well-defined cutoffs. Many real-world tests compromise among these — colonoscopy is highly sensitive and specific but invasive and expensive; FIT is cheap and acceptable but less sensitive. A screening program should offer choices when evidence supports them to maximize uptake.

Sensitivity, Specificity, and Predictive Values

Screening tests must be evaluated for operating characteristics and the impact of prevalence. Sensitivity (true positive rate) and specificity (true negative rate) are intrinsic to the test. Positive predictive value (PPV) and negative predictive value (NPV) depend heavily on prevalence. At low prevalence (screening a healthy population), even a highly specific test yields many false positives — the basis of the "number needed to screen" and "harms of screening" arguments.

Example: a test with 99% sensitivity and 99% specificity applied to a disease with 1% prevalence yields a PPV of only ~50%. Clinicians consistently overestimate PPV when prevalence is low, leading to workups of false positives that cause anxiety, cost, and harm.

17 Adult Screening Recommendations

The USPSTF recommendations below reflect commonly tested adult preventive services. Always consult current recommendations before clinical use — ages and intervals are updated frequently.

Cancer Screening

Cardiovascular & Metabolic

Infectious Disease, Mental Health, Substance Use

Bone, Vision, Other

18 Chemoprevention & Behavioral Counseling

Adult immunization is a core preventive service with lower uptake than childhood immunization in nearly every category. Strategies to improve uptake include standing orders, presumptive recommendations, EHR prompts, pharmacist-delivered vaccines, and removing out-of-pocket cost barriers.

Chemoprevention

USPSTF generally recommends against routine multivitamin supplementation for primary CVD or cancer prevention in average-risk adults. Selective supplementation (folic acid for neural tube defect prevention, vitamin D/calcium in selected populations, iron for deficiency) is still supported by specific indications.

Behavioral Counseling

USPSTF-recommended behavioral counseling interventions include: tobacco cessation (A), healthful diet and physical activity for CVD prevention in adults with risk factors (B), skin cancer prevention in young adults (B), unhealthy alcohol use brief intervention (B), sexually transmitted infection prevention (B), and weight loss interventions (B).

19 Well-Child Care & Bright Futures

Bright Futures is the AAP-authored national health promotion guideline for preventive pediatric care, adopted by HRSA and covered without cost-sharing under the ACA. It specifies the content of well-child visits from birth through age 21.

Developmental Surveillance & Screening Tools

Components of the Well-Child Visit

Key Ages & Topics

• Newborn — metabolic screen, CCHD pulse ox, hearing screen, HepB vaccine, safe sleep (back, alone, crib), breastfeeding support.
• 2–6 months — immunizations, developmental surveillance, postpartum depression screening of mother.
• 9–24 months — ASQ developmental screens, M-CHAT autism 18 & 24 mo, lead at 12 & 24 mo (risk-based), transition to cup.
• 2–6 years — vision and hearing, dental home by age 1, BMI tracking, school readiness.
• Adolescence — HEEADSSS psychosocial interview, Tdap, HPV, MenACWY, annual depression screen, confidential care.

20 Health Behavior Models

Behavior change is the common final pathway of most clinical prevention. Theories of health behavior give clinicians and program designers frameworks for understanding why people do what they do — and how to intervene.

Major Models

Behavior Change Techniques (BCTs)

Susan Michie's taxonomy catalogs 93 discrete behavior change techniques that can be combined into interventions. Common high-evidence BCTs include: goal setting, self-monitoring, action planning, feedback on behavior, problem solving, behavioral contracting, social support, graded tasks, and reviewing outcome goals. Effective interventions typically combine several BCTs rather than relying on information alone. "Just knowing" something rarely changes behavior — skills, supports, and environmental cues matter more.

Motivational Interviewing

Motivational interviewing (MI) is a collaborative, goal-oriented counseling style that elicits and strengthens motivation for change. Core skills use the OARS mnemonic: Open questions, Affirmations, Reflective listening, Summaries. MI is the most evidence-based brief counseling approach for substance use, medication adherence, and weight management.

21 Tobacco, Alcohol, Activity & Nutrition

Stages of Change — Matching the Intervention

Nudge Theory & Choice Architecture

Behavioral economics contributes the concept of choice architecture — the way options are presented strongly influences decisions without restricting freedom. Classic applications in public health: opt-out organ donation, default healthy cafeteria layouts, automatic enrollment in savings plans, salience of calorie labels, and simplified benefit applications. Nudges complement (not replace) structural and policy interventions.

Tobacco Control

Tobacco remains the leading preventable cause of death in the US (> 480,000 deaths/year). The MPOWER framework (WHO) summarizes evidence-based population interventions: Monitor tobacco use, Protect from secondhand smoke, Offer help to quit, Warn about dangers, Enforce advertising bans, Raise taxes. First-line cessation pharmacotherapy: varenicline, nicotine replacement (patch + short-acting combo), bupropion. Counseling + pharmacotherapy roughly doubles quit rates vs. either alone.

Electronic cigarettes and vaping products have complicated tobacco control. They may help some adult smokers quit but introduced nicotine dependence to a new generation of youth. The 2019 EVALI outbreak (vitamin E acetate in THC cartridges) illustrates the risks of unregulated products. The FDA now regulates e-cigarettes as tobacco products with premarket review requirements.

Alcohol

Excessive alcohol use causes ~140,000 US deaths/year. Screening (AUDIT-C, single question) plus brief intervention is USPSTF B-recommended. Pharmacotherapy options: naltrexone, acamprosate, disulfiram. Policy levers with strong evidence: taxes, outlet density restrictions, hours of sale, minimum legal drinking age, impaired driving enforcement.

"Low-risk" drinking guidelines (≤ 2 drinks/day for men, ≤ 1 for women) are increasingly scrutinized as evidence accumulates that no level of alcohol use is clearly beneficial and cancer risk rises linearly from the first drink. Some national guidelines now recommend "less is better" rather than safe thresholds.

Physical Activity

The 2018 Physical Activity Guidelines recommend ≥ 150 min/week moderate OR 75 min vigorous aerobic activity plus muscle-strengthening ≥ 2 days/week for adults; 60 min/day for children. Any amount is better than none; sedentary time independently increases mortality.

Nutrition & Obesity

US adult obesity exceeds 40%; childhood obesity is ~20%. Interventions: dietary counseling (B for CVD risk factors), intensive multicomponent behavioral interventions for obesity (B), sugar-sweetened beverage taxes, menu labeling, WIC/SNAP nutrition policies, school meal standards. Pharmacotherapy (GLP-1 agonists, phentermine-topiramate, naltrexone-bupropion, orlistat) and bariatric surgery complement behavioral change for appropriate patients.

Obesity as a Population Problem

US adult obesity prevalence has more than tripled since the 1960s. Drivers include shifts in food environment (energy-dense processed foods, portion size, marketing to children, sugar-sweetened beverages), decreased physical activity (sedentary work, reduced active transportation), built environment (suburban sprawl, food deserts), sleep deprivation, chronic stress, and endocrine disruptors. Effective population-level interventions include sugar-sweetened beverage taxes, menu calorie labeling, restrictions on marketing to children, school wellness policies, Complete Streets ordinances, and trans fat bans. Individual-level behavior change is necessary but insufficient; environments must support healthy choices.

Opioid Epidemic & Harm Reduction

The US opioid epidemic has unfolded in waves: prescription opioids (1990s–2010), heroin (2010), illicit fentanyl (2013–present). Drug overdose is now the leading cause of injury death in the US (> 100,000 annually). Public health responses combine primary prevention (prescribing guidelines, PDMPs, safe storage/disposal), treatment (expanded MOUD — buprenorphine, methadone, naltrexone), and harm reduction (naloxone distribution, syringe services programs, fentanyl test strips, overdose prevention centers, Good Samaritan laws). Harm reduction accepts that abstinence may not be achievable in the short term and that keeping people alive is a prerequisite to recovery.

22 Air, Water, Food & Toxicants

Air Quality

The EPA's Clean Air Act sets National Ambient Air Quality Standards (NAAQS) for six criteria pollutants: ozone (O₃), particulate matter (PM_2.5, PM₁₀), carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead. PM_2.5 drives most health impact, associated with CV mortality, stroke, lung cancer, and preterm birth. Indoor air concerns include radon (leading cause of lung cancer in nonsmokers), environmental tobacco smoke, combustion byproducts, mold, VOCs, and CO.

Air Quality Index (AQI) & Health Actions

Water Quality

The Safe Drinking Water Act authorizes EPA to set Maximum Contaminant Levels (MCLs). Waterborne outbreaks in the US are rare but continue — Legionella (cooling towers, premise plumbing), Cryptosporidium (chlorine-resistant), and norovirus dominate. Flint, Michigan (2014) demonstrated how corrosion control failures expose populations to lead. Fluoridation (0.7 mg/L) is one of the CDC's "Ten Great Public Health Achievements of the 20th Century."

Food Safety

FoodNet (CDC) provides active surveillance for foodborne illness; PulseNet links whole-genome sequences to detect multi-state outbreaks.

Food Safety — Key Control Points

FDA and USDA oversight is divided: USDA FSIS regulates meat, poultry, and processed eggs; FDA regulates essentially everything else, including seafood and produce. The 2011 FDA Food Safety Modernization Act (FSMA) shifted food safety from reactive response to prevention, requiring Hazard Analysis and Risk-Based Preventive Controls (HARPC) throughout the supply chain. Core food-safety principles taught to the public: clean, separate, cook, chill. HACCP (Hazard Analysis and Critical Control Points) is the industry-standard framework for identifying and controlling hazards at critical steps.

Lead Exposure

Lead is a potent neurotoxin with no safe level in children. Major sources: pre-1978 paint, contaminated soil, drinking water from lead service lines, imported ceramics and cosmetics, some traditional remedies. CDC reference value is 3.5 μg/dL (updated 2021). Risk-based screening at 12 and 24 months via capillary or venous sample; confirm elevated results venously. Treatment: environmental investigation and abatement first; chelation (succimer, EDTA, BAL) only for markedly elevated levels.

23 Climate, Radiation & Vector-Borne Disease

Climate Change & Health

Climate change is called "the greatest health threat of the 21st century" (Lancet Countdown). Pathways: direct heat (heat stroke, CV mortality), worsening air quality (wildfire smoke, ozone), extreme weather (injuries, displacement), changing infectious disease ecology (vector range expansion, waterborne disease), food and water insecurity, and mental health effects. Clinicians increasingly must counsel on heat safety, air quality days, and wildfire preparedness.

Radiation

Principles of radiation protection: time, distance, shielding. Medical imaging is the largest modifiable source of population ionizing radiation — Image Gently (pediatrics) and Image Wisely (adults) campaigns promote dose reduction.

Integrated Vector Management

IVM combines environmental (habitat reduction, drainage), biological (larvivorous fish, Bti), chemical (larvicides, adulticides), and personal protective measures (repellents, nets, housing screens). Over-reliance on any single method breeds resistance. Community engagement is essential — vector control fails without public cooperation in source reduction (standing water on private property).

Heat-Related Illness

Extreme heat kills more Americans than any other weather event. The spectrum runs from heat cramps → heat exhaustion (diaphoresis, tachycardia, core temp < 40°C, mental status preserved) → heat stroke (core temp > 40°C, altered mental status — a medical emergency). Population risk factors: age extremes, chronic disease, anticholinergic/antipsychotic/diuretic medications, social isolation, lack of air conditioning, outdoor occupations. Public health responses include heat-health warning systems, cooling centers, tree canopy and cool roof programs, checks on vulnerable individuals, and regulations protecting outdoor workers.

Vector-Borne Disease

24 Occupational Health & Injury Prevention

Endocrine Disruptors & Emerging Contaminants

PFAS ("forever chemicals"), bisphenol A (BPA), phthalates, pesticides, flame retardants, and certain metals act as endocrine disruptors with effects on thyroid, reproduction, development, and metabolism. Low-dose, long-latency exposures are hard to study, and regulation has lagged the science. PFAS contamination of drinking water affects millions of Americans and led to new EPA maximum contaminant levels in 2024.

Environmental Justice

Environmental justice is the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income in the development, implementation, and enforcement of environmental laws and policies. Documented injustices include disproportionate siting of polluting facilities in communities of color, unequal enforcement, and delayed remediation (e.g., Flint, "Cancer Alley" in Louisiana, "Diesel Death Zones" near freight corridors). Federal Executive Order 12898 (1994) directed agencies to address environmental justice in their missions.

OSHA & NIOSH

OSHA (Department of Labor, 1970) enforces workplace safety standards; NIOSH (within CDC) conducts research and makes recommendations without enforcement authority. OSHA's General Duty Clause requires employers to provide a workplace free from recognized hazards. Permissible Exposure Limits (PELs) cover roughly 500 chemicals; NIOSH Recommended Exposure Limits (RELs) are often more protective but not legally binding.

Hierarchy of Controls

PPE is the least effective control because it depends on individual compliance. Elimination and substitution are most effective because they remove the hazard at its source.

Common Occupational Exposures

Workers' Compensation & Return to Work

Workers' compensation is a state-based no-fault insurance system that provides medical care, wage replacement, and disability benefits for work-related injuries and illnesses. In exchange, employees generally give up the right to sue employers for negligence. Clinicians evaluating work-related conditions must document causation ("more likely than not related to work"), maximum medical improvement, permanent impairment ratings (AMA Guides), and functional restrictions. Early return to work with appropriate accommodations improves long-term outcomes compared with extended absence.

Bloodborne Pathogen Exposures

Healthcare worker needlestick seroconversion risks per percutaneous exposure: HBV ~30% (if HBeAg+ source), HCV ~1.8%, HIV ~0.3%. OSHA's Bloodborne Pathogens Standard (1991) mandates: universal precautions, engineering controls (sharps containers, safer needles), work practice controls, PPE, HepB vaccine offer, post-exposure management, and exposure control plans. Post-exposure: wash, report, source testing, baseline labs, PEP within hours for HIV (tenofovir/emtricitabine + dolutegravir or raltegravir × 28 days), HBIG + vaccine for HBV if not immune.

Injury Prevention — Haddon Matrix

William Haddon's matrix cross-tabulates phases of injury (pre-event, event, post-event) with factors (host, agent/vehicle, physical environment, social environment). It structures comprehensive injury prevention — e.g., a motor vehicle crash analysis considers driver (host), vehicle crashworthiness (agent), road design (physical), and DUI laws (social) across all three phases. Injuries — unintentional and intentional — are the leading cause of death for Americans 1–44.

25 Social Determinants & Health Equity

Social determinants of health (SDOH) are the conditions in which people are born, grow, live, work, and age — the non-medical factors that drive most health outcomes. The WHO estimates that medical care accounts for only 10–20% of modifiable determinants; social and behavioral factors account for the rest.

Healthy People 2030 SDOH Domains

Food Insecurity & Housing Insecurity

Roughly 1 in 8 US households experience food insecurity in a given year; rates are higher among households with children, Black and Hispanic households, and single-parent families. The Hunger Vital Sign (2 items) is a validated clinical screen. Food insecurity is associated with worse control of diabetes, HTN, asthma; higher healthcare costs; and worse child development. Safety-net programs include SNAP (food stamps), WIC, school meals, and CACFP.

Housing insecurity spans a continuum from unaffordable cost burden to eviction to homelessness. Housing is a social determinant — stable housing improves nearly every health outcome. "Housing First" models that provide unconditional supportive housing to chronically homeless people with mental illness or substance use disorders reduce emergency department use and improve housing stability.

Health Equity vs Equality

Equality gives everyone the same thing; equity gives each person what they need to reach the same outcome; justice removes the systemic barriers that make differential allocation necessary in the first place. The goal is health equity: "attainment of the highest level of health for all people" (Healthy People 2030).

Health Disparities & Structural Racism

Documented US disparities include: Black women have a maternal mortality ratio ~3× that of white women; American Indian / Alaska Native populations have the highest diabetes prevalence; Black men have the lowest life expectancy; LGBTQ+ youth face elevated suicide risk. Root causes include residential segregation (redlining), unequal medical treatment (IOM "Unequal Treatment," 2003), wealth gaps, mass incarceration, and chronic stress ("weathering" — Geronimus).

Special Populations

Maternal & Infant Mortality

The US has the highest maternal mortality ratio of any high-income country (~22/100,000 live births; ~3× higher for Black women). Leading causes: cardiovascular conditions, hemorrhage, infection, embolism, hypertensive disorders, and mental health conditions (including suicide and overdose). Key public health responses: Maternal Mortality Review Committees in every state, AIM safety bundles, Medicaid postpartum coverage extension to 12 months, doula access, and addressing implicit bias in maternity care.

Infant mortality (~5.4/1,000 in the US) is driven by prematurity, congenital anomalies, SIDS, maternal complications, and unintentional injury. Black infants die at more than twice the rate of white infants. Interventions: prenatal care, smoking cessation, safe sleep ("ABCs of safe sleep — Alone, Back, Crib"), breastfeeding promotion, home visiting programs, and addressing upstream SDOH.

26 Global Health & Emerging Threats

Global health includes both international cooperation and attention to the health of all people regardless of borders. It differs from "international health" (traditionally focused on LMICs) in scope and ethos — global health considers health threats and solutions shared across nations.

Global Burden

Global health priorities have shifted since 2000. Under-5 mortality has halved; malaria and HIV deaths are declining. But NCDs now cause > 70% of global deaths, and emerging infectious threats continue. The leading causes of global mortality in recent years: ischemic heart disease, stroke, COPD, lower respiratory infections, neonatal conditions, trachea/bronchus/lung cancer, Alzheimer disease, diarrheal diseases, diabetes, kidney disease.

From MDGs to SDGs

The UN Millennium Development Goals (2000–2015) set eight health and development targets. Their successors, the Sustainable Development Goals (2015–2030), include 17 goals; SDG 3 "Good Health and Well-being" contains 13 targets including universal health coverage, ending preventable child and maternal deaths, ending AIDS/TB/malaria epidemics, reducing NCDs, and strengthening health workforces.

Travel Medicine

Global Maternal & Child Health

Despite progress, roughly 287,000 women die each year from pregnancy-related causes globally, almost all in low- and middle-income countries. Leading causes: hemorrhage, hypertensive disorders, sepsis, unsafe abortion, and obstructed labor — all preventable. Skilled birth attendance, emergency obstetric care, family planning, and antenatal/postnatal care are the pillars of maternal health. Child survival gains have come from oral rehydration, vaccines, insecticide-treated nets, exclusive breastfeeding, community case management of pneumonia/diarrhea, and micronutrient supplementation.

Major Global Health Programs

Universal Health Coverage & Global Health Financing

Universal health coverage (UHC) means everyone can use the health services they need, of sufficient quality, without financial hardship. It is SDG target 3.8 and operationalized through the UHC cube: who is covered, what services are covered, and what proportion of costs is covered. Most low- and middle-income countries fund health through a mix of tax revenue, out-of-pocket spending, and donor financing. Out-of-pocket spending > 20% of total health expenditure is associated with catastrophic health expenditure and poverty.

Neglected Tropical Diseases (NTDs)

NTDs are a group of 20+ conditions primarily affecting the world's poorest populations. WHO prioritizes: lymphatic filariasis, onchocerciasis, soil-transmitted helminths, schistosomiasis, trachoma, Chagas disease, leishmaniasis, leprosy, human African trypanosomiasis, dracunculiasis, dengue, rabies, and others. Mass drug administration, vector control, water/sanitation, and health education are the main control strategies; several are targeted for elimination.

Global Health Security

The Global Health Security Agenda (GHSA, 2014) is a multilateral initiative to strengthen IHR core capacities worldwide. The Joint External Evaluation (JEE) tool measures country readiness across prevent/detect/respond domains. Weaknesses persist in surveillance, workforce, laboratory networks, and emergency operations — gaps laid bare by COVID-19.

Emerging Infectious Diseases

Drivers of emergence: deforestation, wildlife trade, intensified agriculture, urbanization, international travel, climate change, and antimicrobial resistance. Recent examples: HIV (1980s), SARS (2003), H1N1 (2009), MERS (2012), Ebola (2014, 2018), Zika (2015), SARS-CoV-2 (2019), mpox (2022). The WHO maintains a priority pathogen "R&D blueprint" list including "Disease X" — an unknown pathogen with pandemic potential.

27 Emergency Preparedness & Bioterrorism

Emergency preparedness is a shared responsibility across federal, state, local, and tribal governments, healthcare systems, private sector, and individuals. The US system is anchored by the National Response Framework and the Pandemic and All-Hazards Preparedness Act (PAHPA) structure.

The Preparedness Cycle

Emergency preparedness follows a continuous cycle: mitigation → preparedness → response → recovery. Each phase has specific public health roles — hazard vulnerability assessment, capacity building and drills, coordinated response, and long-term rebuilding.

Incident Command System (ICS)

ICS is the standardized, modular management structure used for all-hazards response in the US. Core positions: Incident Commander, Operations, Planning, Logistics, Finance/Administration, plus Public Information Officer, Safety Officer, and Liaison. Hospitals use Hospital Incident Command System (HICS). ICS scales from a single ambulance call to a multi-state disaster.

Hazard Vulnerability Assessment & Planning

Every jurisdiction and healthcare facility should conduct regular Hazard Vulnerability Assessments (HVA) scoring probability, severity, and preparedness for each identified hazard. Plans should address all four phases, integrate with regional partners, and be exercised through tabletops and functional drills. The Joint Commission's Emergency Management standards require hospitals to maintain all-hazards plans with 6 critical areas: communications, resources, safety and security, staff responsibilities, utilities, and clinical activities.

Mass Casualty Triage — START

Decontamination

Field decontamination: remove and bag clothing (removes ~80% of contaminant), copious water irrigation, soap if available. Avoid hypothermia. Protect responders with PPE appropriate to the agent. Separate hospital decontamination areas prevent secondary contamination of the ED.

Crisis Standards of Care

When a catastrophic event overwhelms healthcare resources, jurisdictions may formally shift from conventional to contingency to crisis standards of care. Crisis standards allow allocation of scarce resources (ventilators, ICU beds, medications) based on maximizing population benefit rather than individual optimization. Ethical frameworks emphasize transparency, proportionality, equity (not allowing triage scores to amplify existing disparities), accountability, and the duty to plan ahead of crisis. The National Academies' guidance is the touchstone document.

CDC Bioterrorism Categories

CDC Category A Bioterrorism Agents

Public Health Emergency Declarations & Authorities

Risk Communication

Risk communication is the two-way exchange of information about risk between experts and the public. Core principles from Peter Sandman and the CDC: be first, be right, be credible, express empathy, promote action, and show respect. Acknowledge uncertainty rather than overstating confidence; uncertainty disclosed builds trust, while uncertainty hidden and then exposed destroys it. "Don't panic" and "trust us" are among the least effective phrases in a crisis.

Radiological & Chemical Emergencies

28 High-Yield Review & Reference

Core Biostatistical Concepts for Public Health

Confidence intervals express the precision of an estimate; statistically significant results require both a clinically meaningful effect size and adequate power. Public health research increasingly emphasizes effect estimation over null-hypothesis testing, and uses techniques like propensity scoring, instrumental variables, difference-in-differences, and interrupted time series to support causal inference in non-experimental data. Causal diagrams (directed acyclic graphs, DAGs) discipline thinking about confounding and mediation.

Public Health Ethics Frameworks

Public health ethics differs from clinical ethics in that the primary unit of concern is the population, and coercive state power may be exercised for the common good. Classic frameworks (Childress, Gostin, Kass) ask: What is the public health goal? How effective is the proposed intervention? Is it the least infringing option that achieves the goal? Is it proportionate? Is it transparent? Is it equitable? The Siracusa Principles guide human rights considerations during public health emergencies: restrictions must be legally grounded, necessary, proportionate, nondiscriminatory, and limited in duration.

Key Statistics to Remember

Leading Causes of Death by Age Group (US)

Healthy People 2030 — Selected Leading Health Indicators

• Reduce adolescent tobacco and e-cigarette use
• Increase adult physical activity
• Reduce drug overdose deaths
• Reduce suicide rate
• Increase proportion with usual primary care provider
• Reduce household food insecurity
• Increase childhood vaccination coverage
• Reduce maternal mortality
• Reduce infant mortality
• Increase life expectancy

Key Rates & Calculations

Common Public Health Frameworks at a Glance

Glossary of Essential Terms

Landmark Public Health Legislation (US)

Common Board Pitfalls

Students commonly confuse: incidence vs prevalence (new vs existing), sensitivity vs PPV (intrinsic vs prevalence-dependent), RR vs OR (cohort vs case-control), primary vs secondary prevention (before vs after early detection), and lead-time vs length-time bias. Recognizing the setup in the question stem is often more important than memorizing the definitions.

Final Clinical Pearls