Applied Epidemiology

Question 1

What is epidemiology?

Answer 1

The study of disease in populations

Question 2

Define endemic disease

Answer 2

A disease commonly found restricted to one region
Ro < 1
This means that the primary case will infect less than 1 other person/animal

Question 3

Define epidemic disease

Answer 3

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

Question 4

Define prevalence

Answer 4

The proportion of a population that are found (right now) to have this disease

Question 5

Define Incidence

Answer 5

The measure of the probability that a person/animal in a population will get the disease within a given time frame

Question 6

Define morbidity

Answer 6

The number of people/animals in a population that will become ill (incidence) or are already ill (prevalence) at a given time

Question 7

Define mortality

Answer 7

The number of deaths in a population due to a disease

Question 8

Define sensitivity

Answer 8

The ability of a test to correctly identify those with the disease

Question 9

A test with low sensitivity will have ……………… negatives

Answer 9

Many false negatives

Question 10

A test with high sensitivity will have ………………

Answer 10

Few false positives

Question 11

Define specificity

Answer 11

The ability of a test to identify those without the disease

Question 12

A test with a low specificity will have …….

Answer 12

Many false positives

Question 13

A test with a high specificity will have …..

Answer 13

Few false negatives

Question 14

Define positive predictive value

Answer 14

The probability that subjects who have a positive test value actually do have the disease

Question 15

Define negative predictive value

Answer 15

The probability that subjects with a negative test value truly do not have the disease

Question 16

Define accuracy

Answer 16

The degree to which a measurement represents the true value of the attribute being measured

Question 17

What are cohort studies?

Answer 17

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

Question 18

What are hills criteria for establishing cause

Answer 18

Time scale - does the cause precede the effects
Strength of association - cohort studies
Biological association - is there a dose response relationship?
Consistency
Plausability

Question 19

What is the odds ratio?

Answer 19

Odds of contracting the disease in the exposed group vs odds of the disease in the unexposed group

Question 20

What does an odds ratio of > 1 mean?

Answer 20

Risk factor (exposed group) is associated with the disease

Question 21

What is the relative risk?

Answer 21

Ratio of the risk of the disease in the exposed group compared the the unexposed group

Question 22

What molecular techniques can we use to identify the source of a disease?

Answer 22

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

Question 23

Name some advantages of using molecular techniques in epidemiology

Answer 23

Increased sensitivity and specificity of diagnosis
Good for organisms that are difficult to culture
Identification of carriers
Earlier detection, better control and prevention

Question 24

Define disease prevention and disease control

Answer 24

Prevention - stop it happening alltogether
Control - reducing the frequency of the disease to a tolerable level
Disease eradication - eliminating of the disease completely

Question 25

How can we control diseases?

Answer 25

Improved host resistance - eg scrapie serotyping for the ARR resistant ones
Vaccination
Quarrantine/restriction of animal movement
Control of vectors eg ticks
Biosecurity

Question 26

State two methods of disease eradication

Answer 26

Test and removal - eg TB

Preemptive- Cull all animals that have been exposed

Question 27

What are the most common pathogens that cause enteric disease?

Answer 27

1. Campylobacter
2. Clostridium Perfringens
3. Norovirus
4. Salmonella (but most severe)