Intro to Epidemiology Flashcards
Epidemiology
study of distribution and determinants of disease in specified populations and the application of this study to control health problems
Epidemiology focus on groups or individuals
groups
Purpose of epidemiology
ID determinants and describe disease distribution
Veterinary epidemiology
investigates disease, productivity, and welfare in animal populations
Why care about Epi?
evidence based veterinary medicine
provide tools for research
evaluate research
integrate research into practice
Clinical epidemiology approach
-focus on individual (PE, Ddx, Diagnostics..)
-success depends on
known disease & correct Dx
Epidemiological Approach
Focus on groups describe population with and without disease look for differences in groups ID factors Apply measures Success without knowing etiology
John Snow
removed the pump handle
found Cholera outbreak
Descriptive Epidemiology
describe disease (CANNOT infer causality) characteristics, amount, distribution
Describes what in terms of
who, when, where
Analytical Epidemiology
determine assoc. of exposure and outcome in population and how strong association is
(why)
Ultimate goal is determine if exposure factor = disease
the What?
health/ production/ welfare issue of concern
case definition
example: retained placenta in cows
the Who
Age, gender, breed, production type (feedlot/ shelter)
When : time?
changing or stable rates of disease
clustered in time or evenly distributed
single point / intermittent exposure
seasonal variation
Where : place?
geographically restricted or widespread
relation to food/ water supply
clustered or even distributed
one room or whole barn
Association
Dependent
relationship of two measured dependent quantities
- exposure changes and so does amount of disease
Independent (not associated)
- when exposure changes, nothing happens to the
amount of disease
Exposure
any potential determinant of disease or health status
May or May not de determinant
Outcome
result or response
Fundamental axiom of disease
disease are NOT random
disease have causal and preventive factors that can be ID
Cause vs Cause of disease
cause = brings about an effect or result
cause of disease = does not only mean cause
- dz is complex with many causes
- event, condition, character playing an essential roles in producing disease occurrence
Koch’s Postulates if microbes
- always found in individuals with disease
- not found in healthy animals
- can be isolated in pure culture from disease individual
- pure microbe produces same disease in healthy animal
- can be re-isolated from #4
Web of Causation
describes modern disease problems where presence or absence of disease is not just a matter of presence/ absence of pathogens
Epidemiological Triad
host, agent, environment
Disease results form interaction of agent and susceptible host in an environment that supports transmission of agent from source to host
Ken Rothmans (Rothman’s Pies)
general model for representing components causes resulting in disease
Rothmans Pies
Sufficient Cause
each complete pie is a set of component causes that is sufficient to cause disease
Rothman’s Pies
Component cuase
-any one of the component causes of a sufficient cause
(each piece of pie) A - J slices
-not all component causes need to be present in every
sufficient cause
Rothman’s Pies
Necessary cause
component cause that is member of every sufficient cause
slice A is necessary in every pie
Simple cause model of Anthrax
susceptible cattle
Bacillus anthracis spores in soil
DOESNT EXPLAIN OUTBREAK
Sufficient cause of Anthrax
susceptible cattle
Bacillus anthracis spores in soil
excess winter snow and spring rain\
hot, dry summer
Anthrax Sufficent causes with necessary and component causes?
Necessary cause = spores in soil
components spore in soil susceptible cattle, sheep, bison, ... spores in forage excess snow and spring rain dry summer
Rothman Model
completion of sufficient cause is synonymous with occurrence of disease (not diagnoses)
component causes can act far apart in time
a. block action of component cause
b. blocks completion of the sufficient cause
c. preventing disease occurrence by that pathway
How to prove Rothmans model
Does association = Causality
Associations measured can be results of what?
- exposure truly causes outcome
- random error
- systematic error (bias, confounding)
Bradford Hill criteria
temporal relationship
(cause before effect)
assoc. strength
does- response relationship
(more exposure = more disease) ??
replicate findings?
biological plausibility
(does it make sense)
consider alternate explanations
cessation of exposure
(does dz go away when exposure goes away)
specificity of assoc.
consistency
