Applied epidemiology Flashcards
What is epidemiology?
Observing populations and making inferences from these observations
What is veterinary public health?
The part played by vets in human public health, relating chiefly to the recognition and control of zoonotic disease
also mental and emotional well-being
What is an endemic disease
Disease commonly found in, or restricted to a particular region, community or group of people
R0 = Basic reproduction number (reproduction or transmissibility rate)
The average number of cases infected by a primary case when the population is naïve e.g. hasn’t been exposed to a disease (often talked about at the beginning of an outbreak of a novel disease)
For endemic disease, R0 < 1
The average number of cases infected by a primary case is less than 1
What is epidemic disease?
A level of disease in a population significantly greater than usual
R0 > 1
The average number of cases infected by a primary case is greater than 1
What are the approaches to disease investigation?
How many (Number of cases)
- How does it relate to the number ‘normally’ seen?
Are all animals/people at risk (What is the ‘denominator’)?
In which areas (Distribution of disease)?
Over what time (Rates)?
Are there specific subgroups that are more likely to be infected (Who/which)?
Why is the epidemic curve important?
The epidemic curve is important for starting to postulate about cause
The shape of an epidemic curve can give you a preliminary guess at what is causing a problem when you don’t know the cause
Name & describe the two epidemic curves and give some examples
What are Hill’s criteria for establishing the cause of an outbreak
Time sequence – does the cause precede effect?
Strength of association – statistical association between agent and disease?
Biological gradient – is there a dose-response relationship?
Consistency – is an association consistently found?
Coherence or plausibility – is it biologically sensible?
What are common approaches used to determine disease outbreak cause
The following are commonly used to narrow down (or confirm) the possible causes:
Structure/shape of the epidemic curve
Case-control studies
- Compare between cases and non-cases (diseased and non-diseased)
- Look retrospectively at the differences in exposure to risk factors (i.e. calf shed, ice cream)
Cohort studies
- Look retrospectively or prospectively at individuals exposed and not exposed to risk factors (i.e. calf shed, ice cream) and see if they develop disease
What approaches can be used to determine who is at risk (strength of associated) in disease outbreak
How do you calculate the following in disease outbreak:
- odds ratio
- Relative risk
- Risk difference
What is CI
What tests can be done to identify the cause of an outbreak?
Sub-typing genetic material for pathogen identification
An assortment of techniques e.g. RFLP, PCR fingerprinting, DNA sequencing
Amplify targeted pieces/whole of the pathogen’s DNA/RNA in order to determine either speciation (if unknown) or strain identification
Compare the ‘fingerprint’ from human and animal cases and see if they are the same
What are the advantages of sub-typing genetic material for pathogen identification in disease outbreak
Increased sensitivity and specificity of diagnosis
Faster
Good for those organisms that are traditionally difficult to culture (M.bovis and prions)
Outbreaks can be detected and therefore controlled at an earlier stage
Combined with epidemiological evidence, can look to provide evidence of causation
Identification of ‘carriers’
Influence of prevention or control programmes
How can we work out how an outbreak is transmitted
This requires knowledge of the pathogen
Features – and therefore how this relates to pathogen action, transmission routes, optimal environmental conditions etc.
Understanding of a pathogen will alter over time as new information comes to light – particularly when dealing with a novel pathogen
Including what ‘states’ animals/people within your population can be in:
Susceptible (not got disease), Infected (those who have disease), Recovered (those who have had disease), potentially Susceptible again (those who can be re-infected)
