My UGA EPID 4070 (Fundamentals of Epidemiology) Class Notes, 2017

Epidemiology 

Descriptive epi: uses observational studies to describe patterns and frequency of health states and events (person, place, time)

Analytic epi: uses observational studies to identify determinants, associations, causes, and their strength. Testing hypotheses uses experimental studies 

Aims of epi: describe & quantify the health status of populations, explain the etiology/causes of diseases, predict the occurrence of diseases, control the occurrence of disease (CDC)

Epi is interdisciplinary, quantitative, and uses specific vocabulary (cohort, case-control, confounding, odds ratio, bias, etc. )

Epi: health promotion & protection, health and disease surveillance, health inequalities, screening/diagnosis, causes, treatment, prognosis 

Subspecialties: infectious disease, chronic dissed, molecular, environmental, injury, nutrition, behavioral, etc. 

morbidity, mortality, disease/illness, prevalence (new and existing cases, point and period), incidence (new cases in given period of time is cumulative prevalence which is incidence proportion). Prevalence is existing and incidence is new 

Infectious disease is any disease caused by an infectious agent (virus, bacteria, parasites). Example HIV, influenza, Ebola, polio 

Case = person diagnosed with disease  disorder injury or condition (person, place, time)

Case definition: replicable, explicit (balance, speed, practicality, cost). Flu fast diagnosis looks at fever + cough symptoms. Slower more accurate uses positive lab PCR test

Suspected case vs. confirmed case 

Primary case = first case in population 

Index case = first seen by epidemiologist

Secondary case = anyone affected after introduction of disease 

Endemic - ongoing, constant, prevailing, 

usual presence of disease in region 

Epidemic - occurrence of event/state above expected 

Pandemic - epidemic affection very large area

These 3 terms describe the extent. 

Common source - all/most cases infected by same source (point: short time, intermittent: recurring, continuous: prolonged time)

Propagated - communicable disease (TB, HIV, flu), person-to-person, can be direct or indirect 

Mixed - like typhoid fever, usually food-borne illness, mixes common source and propagated

Direct transmission vs. indirect transmission (fomites, airborne, vector)

Fomites: inanimate object 

Vector: invertebrate animals 

Reservoir: habitat in which infectious agent lives, grows, and multiplies (humans often both host and reservoir). Portal of entry and exit 

Carrier

Epi triangle for understanding spread of infectious disease (agent causes disease, host is organism that harbors disease, environment is external to host, time means incubation or duration of illness and life experience of host or agent)

Advanced triangle focuses on primary problem facing world today, not infectious disease, chronic disease (causal factors, populations and their characteristics, environment behavior culture physiology ecology)

Often multiple factors lead to outcome (multifactorial etiology), there are necessary factors. 

Primary prevention: before it happens 

Secondary prevention: screening/detection 

Tertiary prevention: stops progression of condition (included rehab)

Active vs. passive primary prevention 

Efficacy: ability of intervention to produce desired outcome in ideal world 

Effective: same ability in real world (factors in cost)

History of epi

Hippocrates - father of medicine, first epidemiologist, emphasized observation, saw role of geography environment water quality, rational basis instead of supernatural 

Sydenham - classified fevers in London in 1600s, advanced advice about diet, health, fresh air 

Lind - observed scurvy and conducted experiment with diet, first clinical trial, discovered positive effect of citrus 

Jesty - English dairy farmer, found those with cowpox were immune to smallpox, like a vaccine

Edward Jenner - invented vaccine for smallpox 

Ignaz Semmelweis - found childbirth fever was caused by poor sanitation between pelvic examinations 

John Snow - father of modern epi, studied cholera, physician of Queen Victoria, discovered Broad Street pump as source of contamination 

Louis Pasteur - identified cause of rabies, learned about anthrax transmission from underground, developed anthrax vaccine 

Robert Koch - took first photos of microbes, identified cause of TB, found cholera bacteria, promoted good water filtration, won Nobel prize, 4 postulates 

John Graunt - began recording vital statistics (cause location age sex person who died)

Ramazzini - occupational health 

Case-control study: cases have it, controls don't 

Cohort study: follows group w/o disease to see if they develop (Framingham study)