MODULE 2 - Epidemiology of Infectious Diseases and Principles of Antimicrobial Therapy Flashcards
what is epidemiology?
the study of distribution and determinants of health-related states or events (including disease) in specified populations and the application of this study to the control of disease and other health problems
what does epidemiology involve?
counting cases or health events and describes them in terms of time, place and person
dividing the number of cases by appropriate denominator to calc rates
comparing these rates over time or for different groups of people
what are the 5 W’s of epidemiology?
what - health issue of concern (case definition)
who - person (age, gender, ethnicity etc.)
where - place
when - time
why/how - causes, risk factors, modes of transmission
first 4 are descriptive epidemiology, 5th is analytical epidemiology
what is cholera?
acute diarrhoea illness which can lead to dehydration, coma and death
intestinal infection with vibrio cholera and transmission by contaminated food or water
how is frequency (how many) important to epidemiology?
relationship of no. of health events to population size allows comparison of disease occurrence across different populations
measures are prevalence and incidence
how is pattern important to epidemiology?
occurrence of health events by time (when), place (where), and person (who)
what is prevalence?
the proportion of a population that have the disease at a given point in time (i.e. existing cases)
how do you calculate prevalence?
prevalence = number w disease/total number in population
what is incidence proportion?
proportion of people who develop a disease during a specified time period (i.e. new cases)
how do you calculate incidence proportion?
incidence proportion = number who develop disease during a time period/total number at risk at the start of time period
what is the incidence rate?
how quickly people are developing the disease (i.e. new cases)
how do you calculate the incidence rate?
incidence rate = number of people who develop disease during time period/number of person-years at risk
what are determinants?
the causes and other factors that influence the occurrence of disease and other health-related events
i.e. identify the risk factor which leads to the disease via a causal pathway
what measures are associated with determinants?
relative risk
risk difference/attributable risk
odds ratio
what is relative risk (risk ratio) and how do you calculate it?
relative risk = incidence in exposed group/incidence in non-exposed group
how do you calculate the risk difference?
incidence of exposed group MINUS incidence of comparison group
when would you use an odds ratio?
when you don’t know the number of people exposed and is risk cannot be calculated
how do you calculate an odds ratio?
odds of exposure = number of exposures/number of non-exposures
odds ratio = odds of exposure in cases/odds of exposure in controls
what are the two main types of studies in epidemiology?
observational (cross-sectional, cohort, case-control)
experimental (randomised controlled trials)
what is a cross-sectional study?
observational
randomly select sample of source population
at same point in time measure exposures of interest and outcome of interest
calculate prevalence of exposures and outcomes
descriptive only
what is a cohort study?
observational
randomly select a sample of source population
measure exposure state of participants at beginning of study
group participants by exposed or not
follow-up for period of time
count who develops the outcome during follow-up
calculate incidence, relative risk and risk difference
what is a case control study?
observational
select cases with outcome of interest
select controls (without the outcome of interest) from the same source population
measure exposure status of both cases and controls
calculate odds ratio
what is a randomised controlled trial?
experimental
randomly select a sample of the source population
randomise sample participants into groups (intervention or control)
follow-up participants for period of time
measure outcome
calculate incidence, relative risk, and risk difference
what is a confounding factor?
a third variable distorting results
independently associated with exposure or outcome
does not sit on causal pathway