Introduction to Epidemiology Flashcards
Epidemiology
Science of study and analysis of the distribution (who, when, and where) and determinants of health and disease conditions in defined populations`
Epidemiology purposes
Discover, Determine, Identify, Evaluate
Discover
Discover the agent, host, and environmental factors that affect health
Determine
Determine the relative importance of causes of illness, disability, and death
Identify
Identify those segments of the population that have the greatest risk from specific causes of ill health
Evaluate
Evaluate the effectiveness of health programs and services in improving population health
Does epidemiology refer exclusively to the study of infectious diseases in population?
No Infectious diseases Injuries Cardiovascular diseases Cancers Lead poisoning
Individual approach
Diagnosis —> treatment
Diagnostic process
Anamnesis (verbal history) Critical signs Hypothesis=differential diagnosis Test (lab) Diagnosis Treatment and prevention
Might have to go back and forth a few times when you first start out
Use of epidemiology in anamnesis
To describe a condition: three essential characteristics of disease
Who, When, Where
Importance of epidemiology in veterinary practive
Risk of skin cancer in white cats
Hip dysplasia prevalence higher in german shepherds
Transmission of ringworm by contact
Bovine respiratory disease with peak in fall
Risk of lyme disease in hunting dogs
Spirocerca lupi in southern USA
Susceptible host
Breed, age, sex
Environment
Housing management Population density Nutrition Season Prevention
Epidemiological approach
What is the problem? (outcome surveillance)
What is the cause? (exposure, risk factor)
What works? (intervention, Evaluation)
How do you do it? (implementation)
Prevention
Stop it from infecting population
Control
Measures to reduce infections (social distance)
Recent research on epidemiology
Have focused on non communicable disease -impact of smoking -cancer -cardio-vascular diseases -obesity Emerging disease zoonoses
Study Design: Analytical vs Descriptive
What groups were compared?
Analytical: ages of multiple classes
Descriptive: ages of one class
Study Design: Experimental vs Observational
Had the researchers any control on variables?
Observational (age/sex of group)
Study Design: Cross-sectional vs cohort
How many times were individuals observed?
Cross sectional: blood from shelter one time
Cohort: blood multiple times- go back a month later
Study Design: Prospective vs retrospective
Forward of backwards timeline?
Prospective: blood today and a month later
Retrospective: get records-past
Measure of disease frequency: rates
Numerator: number of animals to whom something happened during a period of time
Denominator: the population at risk during this period of time
Mortality rate, Incidence rate
Surverillance
Ongoing systematic collection, analysis, and interpretation of health data
Compartment model of infectious disease
SIR model
Susceptible, Infected, Infectious shedder, diseased, Recovered, carrier, dead
Latent period
Time from infection to infectiousness. The pathogen replicates in the host but is not shed yet
(from infected to infectious shedder)
Infectious period
The pathogen is shed by the individual
from infectious shedder to recovered
Incubation period
Time from infection to onset of the disease. The pathogen replicates but no clinical signs are observed
(from infected to diseased)
Symptomatic period
Observation of clinical signs
from diseased to recovered
Epidemic
Excessive occurrence of a disease in a particular geographical region
Epizootic
Endemic
Disease that is habitually present in a particular geographical region
Enzootic
Pandemic
Epidemic at worldwide scale
Panzootic
Four Postulates
- Must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms
- Must be isolated from a diseased organism and grown in pure culture
- The cultured microorganism should cause disease when introduced into a healthy organism
- Must be re-isolated from the inoculated, diseased experimental host and identifies as being identical to the original specific causative agent
Strength of association
The stronger the association between a risk factor and outcome, the more likely the relationship is to be causal
Consistency of findings
Have the same findings been observed among different populations, in different study designs and different times
Specificity of the association
There must be a one to one relationship between cause and outcome
Temporal sequence of association
Exposure must precede outcome
Biological gradient
Change in disease rates should follow from corresponding changes in exposure (dose-response)
Biological plausibility
Presence of a potential biological mechanism
Coherence
Does the relationship agree with the current knowledge of the natural history/biology of the disease
Experiment
Does the removal of the exposure alter the frequency of the outcome
