Field that studies distribution & timing of diseases (infectious & non-infectious); determines etiology, transmission, and susceptible populations

study of the causes of disease

of individuals w/ disease

#/pop; %

of deaths from disease

#/pop; %

no. individuals at certain time

no. of new cases

Sporadic, Endemic, Epidemic, Pandemic

occurs occasionally w/o regional concentration (random) i.e. Tetanus, rabies, plague

constantly present in certain region (usually at low levels) i.e. Malaria, Ebola, chicken pox

larger than normal amount of cases i.e. Influenza, West Nile

epidemic that is cross continental i.e. Virulent influenza, Ebola, etc. (COVID)

All cases MUST be reported by physicians Ex: West Nile, HIV, measles, etc. Studies track notifiable disease to determine risks

publishes Morbidity and Mortality Weekly Report (MMWR) Provides physicians and health-care workers with updates on public health issues and latest data on notifiable diseases

father of epidemiology; cholera in London 1854

Determined many deaths were from poor sanitation, not battle

used epidemiology data of handwashing for better healthcare practices (carbolic acid/aseptic conditions)

single source for all infected indiv. Broad Street water pump

common source that exists for short-time (< pathogen incubation) potato salad

continuous contamination sewage from upstream of cholera in London

on and off rainfall runoff

direct or indirect person to person contact no single source

not manipulated Descriptive Analytical Cohort Method Case-control Cross-sectional

subjects are manipulated; clinical trials; ethical concern, best evidence for etiology, double-blind studies

gathers info about disease outbreak

• Includes interviews & examination of medical records (family history)

• Helps develop hypothesis for etiology/causation

selects group to evaluate hypothesis Retrospective – data from past groups (history)

Prospective – date from current subjects moving forward (looking at it as it is going forward

group-based examines individuals who share a particular characteristic Prospective or retrospective

group-based compares groups w/ disease to group w/o Commonly retrospective

group-based group is randomly selected, compares disease and no disease at a point in time Looks for associations of measurable variable(s) and the disease

soil, water; Ex. Clostridium spp. in soil

humans, animals; Ex. Viruses, enteric microbes

living reservoirs (Long persisting pathogens must live somewhere)

transmits mechanically; is not infected - failing to wash hands

infected host transmits during incubation or convalescence - transmission before/after fever Asymptomatic – active carrier w/o symptoms - early HIV, typhoid Mary aka Mary Mallon

Parasitic infection: preferred host; parasite reaches sexual maturity

Parasitic infection: can include one or more; parasite goes through immature life cycle stages

Direct contact transmission – person to person - Vertical – mother to child - Horizontal – other person to person contact - Droplet – transmission in droplets at 1 meter or less Indirect contact transmission – fomite to person - Ex. Sexually transmitted = direct & horizontal - Ex. Birth = direct & vertical - Ex. Cough @ short range = direct & droplet - Ex. Cough onto desk = indirect

through water, food, or air Ex. Aerosols; Hantavirus Ex. Longer lasting droplets; tuberculosis

animal vector (not infected) carries pathogen from one host to another; - Mechanical vector ; Ex. fly that lands on feces & food,arthropod

pathogen reproduces in vector that transmits pathogen from one host to another - Biological vector ; Ex. mosquitoes that pick up West Nile

isolation of infected or exposed individuals to prevent transmission of the disease - Duration is determined by incubation period & evidence of infection

Nosocomial: Commonly introduced through contaminated medical equipment (e.g. catheters, respiratory ventilators, etc.)

WHO, CDC, EU Health Security Committee - Provide logistical support and response in case of epidemic/pandemic - Identify emerging & re-emerging diseases

new to population or shown increase in prevalence in last 20 yrs Ex: Ebola (2015), Coronavirus (2020)

increase after period of decline Ex: drug resistant tuberculosis Ex: measles; decline in vaccinations