--- module: 065-01 language: en chapter: 65 title: "Epidemiology, Screening, Vaccination, Prevention, and Population Health" module_title: "Foundations" source_sha256: fa0b76b8691084e109bf9556cec701639cafea7d55043dec38909a46a4faf175 --- # Epidemiology, screening, vaccination, and population health ## Orientation ### Why disease occurs unevenly ### Housing, income, education, food, work, access #### Determine illness and recovery ### Evidence with fairness, feasibility, trust, harm ## Measures of disease ### Incidence: new events among people at risk ### Prevalence: existing disease at point or period #### Depends on incidence and duration #### Chronic survivable disease: high prevalence ### Case fatality: diagnosed cases who die ### Risk is probability, rate uses person-time ### Absolute difference versus relative ratio #### Rare outcome: large relative, small absolute ### Number needed to treat: 1 / absolute reduction #### State time horizon and baseline risk ### Standardisation depends on chosen reference ### Ecological data cannot apply to individuals ## Prevention levels ### Primordial: prevents emergence of risk ### Primary: prevents disease before onset ### Secondary: early detection and prompt treatment ### Tertiary: limits complication and disability ### Quaternary: protects from unnecessary intervention ### Upstream measures reach more than counselling #### Safe water needs no repeated individual choice #### Taxes and labelling should avoid regressive burden ## Screening principles ### Aim is less morbidity or mortality ### Needs detectable preclinical phase #### Effective earlier treatment and defined pathway ### Low prevalence: false positives outnumber true ### Harms: anxiety, follow-up, overdiagnosis ### Length bias favours slow disease ### Lead-time bias lengthens apparent survival #### Randomised outcomes beat stage shift ### Sensitive test, then specific confirmation ### Programme can widen inequity ### Opportunistic testing without follow-up fails ## Vaccination and immune protection ### Antigen exposure creates memory B and T cells ### Conjugation recruits T-cell help ### Adjuvants enhance innate signalling ### Effectiveness varies with host and pathogen #### Severe disease prevented better than infection ### Herd threshold varies with transmissibility ### Events after vaccination not necessarily caused #### Compare background rates, timing, mechanism ### Live vaccines replicate #### Avoided in severe immune suppression, pregnancy ### Vaccinate before immune-suppressive treatment ### Missed doses continue, not restart ## Cardiovascular and metabolic prevention ### Estimate absolute cardiovascular risk #### Risk factors act together ### Accurate, repeated blood-pressure measurement ### Lipid benefit follows baseline risk ### Statin effects evaluated, prevention kept ### Antiplatelet: bleeding outweighs low-risk benefit ### Obesity care avoids stigma ### Adjust goals for frailty and life expectancy ## Cancer prevention and early detection ### Tobacco control prevents multiple cancers ### Papillomavirus and hepatitis B vaccination ### Chemoprevention only if risk justifies harm ### Cervical, breast, colorectal, lung programmes ### A test existing is not a reason to screen #### Thyroid, ovarian, pancreatic overdiagnosis ## Infectious-disease prevention ### Match precautions to transmission route ### Protective equipment is one layer only #### Fails with poor systems, ventilation, staffing ### Antimicrobial resistance from shared exposure #### Narrow therapy, correct dose and duration #### No antibiotics for viral illness ### One Health: shared ecosystems ## Tobacco, alcohol, and substance prevention ### Behavioural support plus pharmacotherapy ### Long-acting plus short-acting nicotine ### Relapse prompts support, not blame ### Alcohol risk varies by dose and pattern ### Naloxone and agonist treatment reduce death ## Health equity and implementation ### Equal gives same resource ### Equitable responds to barriers and need ### Identity is not biology ### Community co-design builds trust ### Evaluate reach, uptake, harm, distribution ### Healthier choices made practical and ordinary