Applied Epidemiology Flashcards
What is epidemiology?
The study of disease in populations
Define endemic disease
A disease commonly found restricted to one region
Ro < 1
This means that the primary case will infect less than 1 other person/animal
Define epidemic disease
A level of disease in a population significant greater than usual
Ro>1
The average number of people/animals infected by each case is more than 1
Define prevalence
The proportion of a population that are found (right now) to have this disease
Define Incidence
The measure of the probability that a person/animal in a population will get the disease within a given time frame
Define morbidity
The number of people/animals in a population that will become ill (incidence) or are already ill (prevalence) at a given time
Define mortality
The number of deaths in a population due to a disease
Define sensitivity
The ability of a test to correctly identify those with the disease
A test with low sensitivity will have ……………… negatives
Many false negatives
A test with high sensitivity will have ………………
Few false positives
Define specificity
The ability of a test to identify those without the disease
A test with a low specificity will have …….
Many false positives
A test with a high specificity will have …..
Few false negatives
Define positive predictive value
The probability that subjects who have a positive test value actually do have the disease
Define negative predictive value
The probability that subjects with a negative test value truly do not have the disease
Define accuracy
The degree to which a measurement represents the true value of the attribute being measured
What are cohort studies?
They look retrospectively at those who were exposed and those who were not exposed to risk factors (eg. bats) and which ones developed the disease
What are hills criteria for establishing cause
Time scale - does the cause precede the effects
Strength of association - cohort studies
Biological association - is there a dose response relationship?
Consistency
Plausability
What is the odds ratio?
Odds of contracting the disease in the exposed group vs odds of the disease in the unexposed group
What does an odds ratio of > 1 mean?
Risk factor (exposed group) is associated with the disease
What is the relative risk?
Ratio of the risk of the disease in the exposed group compared the the unexposed group
What molecular techniques can we use to identify the source of a disease?
PCR fingerprinting, DNA sequencing
Amplifiying targeted pieces of DNA to determine speciation or strain
Comparing the fingerprint from human and animal cases to see if they are the same
Name some advantages of using molecular techniques in epidemiology
Increased sensitivity and specificity of diagnosis
Good for organisms that are difficult to culture
Identification of carriers
Earlier detection, better control and prevention
Define disease prevention and disease control
Prevention - stop it happening alltogether
Control - reducing the frequency of the disease to a tolerable level
Disease eradication - eliminating of the disease completely
How can we control diseases?
Improved host resistance - eg scrapie serotyping for the ARR resistant ones
Vaccination
Quarrantine/restriction of animal movement
Control of vectors eg ticks
Biosecurity
State two methods of disease eradication
Test and removal - eg TB
Preemptive- Cull all animals that have been exposed
What are the most common pathogens that cause enteric disease?
- Campylobacter
- Clostridium Perfringens
- Norovirus
- Salmonella (but most severe)
