midterm Flashcards
epidemiologic triad
host, agent, environment, vector
endemic
usual disease occurrence in a geographic area
outbreak
unexpected increase in endemic disease cases
epidemic
in excess of normal disease cases
passive surveillance
often voluntary reporting, “chance favors the prepared mind”
active surveillance
mandatory or regular reporting in a defined population
direct transmission
person-to-person, e.g. sneezing, aerosolized, fluid
indirect transmission
transmission through intermediates, e.g. common vehicle (water for cholera), vector (mosquitos for yellow fever), or zoonotic reservoir (pets and lyme)
types of diffusion
expansion/contact and relocation
types of disease cases
index (first to be identified), primary (brings infection to a population), secondary (infected by a primary case), tertiary (infected by a secondary case)
epidemic curve components
infusion (small proportion infected), inflection (rapid increase in infecteds), saturation (decrease in susceptibles), waning (decrease in infecteds)
epidemic curve types
one incubation period (single peak), multiple incubation periods (consistent levels over time), multiple waves (multiple peaks)
contagiousness/attack rate definition
likelihood that infection will be transmitted
attack rate formula
of people at risk who develop disease / # of total people at risk
case fatality rate definition
likelihood of dying once you have the disease
case fatality rate formula
(# of deaths from a disease / # of diagnosed cases of that disease) * 100
reproductive rate
average number of people infected by one infectious individual (R0)
R0 < 1 = the infection will eventually disappear
R0 > 1 = the infection will be able to spread in the population
dispersion factor
small number of highly infectious people disproportionately impact the number of secondary cases (K)
incubation period
time period between exposure and onset of disease symptoms
communicable period
time during which a pathogenic agent may be transmitted
SEIR model
susceptible (yet to be infected)
exposed (latent infected, not yet transmitting –> dead ends never become infectious)
infectious (actively able to transmit; carriers)
recovered (immune/can no longer develop disease)
herd immunity
increase the immune population, reduces rate by interrupting chain of transmission. you do NOT need to immunize 100% of the population
prevalence (formula)
(# of cases of a disease present in a population at a specified time / # of persons in the population at that specified time) * 100
cumulative incidence formula
of new cases / # of persons at risk at beginning time period
incidence rate formula
IR
of new cases during the time period / total person-time of observation
relative risk or rate/risk ratio formula
RR
incidence of disease in the exposed / incidence of disease in the unexposed
(a / a+b) / (c / c+d)
attributable risk formula
AR
incidence of disease in the exposed - incidence of disease in the unexposed
(a / a+b) - (c / c+d)
attributable risk percent formula
AR%
(AR / incidence of disease in the exposed) * 100
(Ie - Io) / Ie *100
population attributable risk formula
PAR
incidence in total - incidence among unexposed
population attributable risk formula
PAR%
(PAR / incidence in total) * 100
cause definition
X causes disease for an individual if and only if the individual has X and gets the disease, and at the same moment in time with all else equal, the same individual would not have gotten the disease without X
mackie’s counterfactual definition of cause
X and Y occurred and, within a causal field, in the circumstances, Y would not have occurred if X had not at least when and how it did
rothman’s definition of a cause
a cause of a disease is an event, condition, or characteristic that preceded the disease event and without which the disease event would not have occurred at all or would not have occurred until some later time
risks that result in association and not causation
reverse causation, noncomparabilty/confounding, study artifacts (chance, selection bias, misclassification)
necessary cause
cannot get disease without it. in the pie model, it is present in all pies
sufficient cause
when all components are present, disease will occur. in the pie model, the entire pie is required
INUS causes
insufficient but
necessary component of
unnecessary but
sufficient cause
randomized controlled trial features
RCT
- a prospective study in humans using randomization to compare the effect of an intervention against a control
- random assignments of exposure/nonexposure in a group of individuals that are otherwise the same
as-treated definition
evaluating data based on which group each participant fell in based on participant behavior (ie if a participant failed to keep up with exposure, assign them to nonexposure). not recommended to do because it eliminates comparability by introducing selection bias
intent-to-treat definition
evaluating data based on which group each participant was assigned to, regardless of whether they followed through. recommended because it maintains comparability between groups
