epidemiology terms

what is epidemiology?

study of the determinants & distribution of health-related states or events in human populations, & application of this study to prevent & control health problems

determinants of epidemiology

etiology, risk factors, protective factors, & modes of transmission (what & how)

determinants - causes/risk factors

• tobacco use

• alcohol

• environmental causes

• genes

social determinants of health (more environmental)

conditions in the environment where ppl are born, live, learn, work …

distribution

• who

  • person/population

• where

  • location/geography

• when

  • time

prevention & control

population-based interventions vs high-risk interventions

inform clinical practice

drive policy

primary prevention

• preventing disease before it happens

  • healthy individuals

  • promote healthy behaviors

secondary prevention

• catching disease at an early, asymptomatic stage

  • requires knowledge of the natural history of the disease

tertiary prevention

• use treatment & care to manage disease & improve quality of life

  • preventing complications

  • requires clinical data

testing all the incoming college students for SARS-CoV-2

secondary

wearing a mask to prevent acquisition of a respiratory infection is an example of what tye of prevention?

primary

wearing a seatbelt that can prevent severe injury or death is an example of what type of prevention?

primary

rabies post-exposure prophylaxis which includes immunoglobulin & vaccine administration is an example of what type of prevention?

secondary

passive surveillance

• health juridictions receive reports submitted from hospitals, clinicals, public health units, or other sources

active surveillance

• health jurisdictions proactively collect disease data from labs, health care providers, or the general public

modes of transmission

• direct

• indirect

direct transmission

• occurs when there is physical contact between an infected person & a susceptible person

  • skin to kiss

  • kissing

indirect transmission

• occurs when there is no direct human-to-human contact; may occur from a reservoir, contaminated objects or vectors

  • blood-borne (via needle)

endemic

usual presence of disease within an area or population

epidemic

disease in excess of what would normally be expected

outbreak

epidemic in a defined community, geographical area, time period

pandemic

epidemic involving several countries of continents, affecting a large population

infectivity

ability to infect

• number of infected/number of susceptible

pathogenicity

ability to cause disease (harm to the host)

• number with clinical disease/number of infected

virulence

ability to cause death, degree of pathogenicity

• number of deaths/number with clinical disease

stages of disease (of the host)

• incubation period

• prodromal period (non-specfic symptoms)

• period of illness (disease-specific symptoms)

• convalescence (asymptomatic)

• latent

• infectious phrase

incubation period (asymptomatic)

• initial stage of the disease process before symptoms become apparent

• no signs/symptoms

prodromal period (non-specific symptoms)

• stages of the disease process when symptoms first become apparent

• symptoms are non-specific

period of illness (disease-specific symptoms)

• aggregate effects of a pathogen produce specific symptoms & their localizations provide diagnostic information

convalescence (asymptomatic)

• when symptoms disappear (recovery period)

latent period

• represents the time of infection to the time of becoming infectious

infectious period

• represents the time after the latent phase when there is enough of the replicating pathogen to be able to transit to another susceptible host

transmission period

mean number of individuals directly infected by a case when introduced to a susceptible person

how do we interrupt transmission?

• direct

  • minimize touching/kissing

  • condoms

  • good hygiene

• indirect

  • PPE

  • shelter in place

how do we achieve herd immunity?

• vaccination as a method of breaking the chain of transmission - establish herd immunity

approach to exploring etiology

• determine if there is an association

• if an association is demonstrated, determine whether the observed association is likely to be a casual one

two variables can have a casual relationship but not be associated

1. true

2. false - (if there is no attraction there is no relationship)

casual relationship summary

• necessary: without the factor the disease never develops (factor is necessary)

• sufficient: in the presence of the factor alone, the disease always develops

how do we establishz causality?

• necessary & sufficient

• necessary but not sufficient

• sufficient but not necessary

• neither sufficient nor necessary

casual relationship 1

NECESSARY & SUFFICIENT

• without that factor, the disease never develops (the factor is NECESSARY), & in the presence of that factor, the disease always develops (the factor is sufficient);

casual relationship 2

NECESSARY but not SUFFICIENT

• each factor is necessary but not in itself sufficient to cause disease;

• there are other factors needed to cause disease

casual relationshipc 3

SUFFICIENT but not NECESSARY

• the factor alone can cause disease, but so can other factors that are acting alone

casual relationship 4

neither SUFFICIENT nor NECESSARY

• probably the most complex model, where multiple factors in combination with others can cause disease

hill’s criteria for assessing evidence of causality

• strength of association

• consistency

• specificity

• temporality

• biological gradient or dose-response

• plausibility

• coherence

• experiment

• analogy

strength of association

starts from the premise than an association is statistically significant between those who have the disease & the comparator group

consistency

specificity

factor that is likely to be causative of disease if the disease occurs within a specific population and/or at a specific anatomical site with no reasonable explanation

temporality

describes the casual timeline, where the risk factor/exposure must [recede the disease/outcome]

biological gradient or dose-response

focuses on the risk factor/behavior in question & it’s relationship with incidence or prevalence of the outcome

plausibility

requires that the association between a risk factor/exposure & the disease/outcome can be explained (feasibility) in the presence of existing biological or social models

coherence

requires that the interpretation of the data not seriously conflict with what is already known about the disease/outcome or risk factor/exposure

experiment

analogy

when there is strong evidence of a casual relationship between a particular agent & a specific disease, researchers should be more accepting of weaker evidence that a similar agent may cause a similar disease

directed acrylic graphs (DAGS)

• intuitive yet rigorous tool to communicate about casual questions in clinical & epidemiologic research & inform study design & are statistical analysis

• constructed to depict prior knowledge about biological & behavioral systems related to specific causal research questions

directed

all variables in the graph are connected by directional arrow

acyclical

if you start at a variable X, following the arrows should not lead back to X

graph

presence of nodes that represent factors/variables & arrows that represent casual effects of one factor on another

mediator

is an intermediate variable that lies on the causal pathway between two variables

confounder

is the existence of an open backdoor path between two variables

collider

is a node where two nodes meet

A case-control study comparing history of Zika infection among mothers of infants with microcephaly compared to matched controls (mothers of infants without microcephaly) found the odds a baby having microcephaly was 14 times higher among mothers who had a Zika virus infection during pregnancy than those that did not.

D. strength of association