Measuring Disease

Question 1

3 components of disease surveillance systems?

Answer 1

1. Defined disease monitoring system
2. A defined level or threshold of disease at which an intervention should take place
3. Defined set of interventions that will be undertaken if and when the threshold is reached

Question 2

What is passive surveillance>

Answer 2

A fixed routine method that typically involves examining clinical cases

ie. diagnostice laboratory data to determine the number of cases of salmonella

Question 3

What are the disadvantage of passive surveillance systems?

Answer 3

Samples not representative of entire pop

Low prevalence diseases are not suited to passive surveillance

Question 4

What is active surveillance?

Answer 4

Purposeful collection of information oftern targeting a specific disease

Question 5

Compare and Contrast active to passive surveillance

Answer 5

Active

• More expensive
• More acurate estimate of disease frequency

Question 6

What is called when everyone is sampled?

Answer 6

Census

Question 7

What is random sampling?

Non-random?

Answer 7

Random - every member of the pop has equal chance of being sampled

Non-Random : Target specific groups or farms

Question 8

What is Targeted surveillance?

Answer 8

BSE

Diseases which are rare - random sampling would be very inefficient for finding cases

Targets high risk animals

4Ds : Diseased, Down, Dying or Dead

Question 9

What is sentinel surveillance?

Answer 9

Non-random targeted surveillance

Canary in the coal mine

Question 10

What are sentinel units?

Answer 10

Herds, vet clinics, flocks are chosen to intensively monitor over a period of time

• Measure frequency of diseae
• Early warning system

Question 11

What is syndromic surveillance?

Answer 11

Group clinical diseases into syndromes rather than specific diagnosis ie. Neurological disease)

Watch pop for sudden increase in reports of specific syndromes

Question 12

4 reasons why we perform disease surveillance

Answer 12

1. Understand the amount or distribuitoin of disease
2. Protect public health by rapid detection and prevention of diseae
3. Market access and international trade
4. Detect emerging diseases

Question 13

3 reasons why we perform disease surveillance

Answer 13

1. Detect emerging diseases
2. Analyze effectiveness of disease control/eradication measures and biosecurity programs
3. Early warning systems

Question 14

6 Challenges in building good surveilance systems

Answer 14

1. Buy in and participation
2. Data integration and analysis
3. Confidentiality and data sharing
4. Maintaining vigilance
5. Convincing practitioners of the value of the information they are collecting
6. Diagnostic tests for identifying disease

Question 15

What is prevalence?

Answer 15

The proportion of cases or infections in the population at one particular time

• no distinction between old and new cases

Question 16

What does prevalence represent?

Answer 16

Probability of an animal being infected at a given time

Question 17

What is incidence?

Answer 17

of new cases in period of time/total populat at risk

• Takes into account new cases only
• Measure of the risk of becoming a case during a defined time period

Question 18

Cumulative Incidence equation

Answer 18

CI = # of individuals that become diseased during a certain period of time / # of healthy individuals in the pop at the beginning of that period

Question 19

What type of population is best for cumulative incidence?

Answer 19

Static pops

Question 20

What occurs to CI when non-diseased animals leave the population during the measured time period?

Answer 20

Half of the withdrawals are subtracted from deominator

Question 21

What does incidence rate meaure?

Answer 21

The rapidity with which new cases develop over time

Question 22

What is the incidence rate equation?

Answer 22

I = # of new cases of disease that occur in a pop during a particular period of time / ((# at risk at the start of the time period + # at risk at end) / 2)

Question 23

Attack Rate Equation

Answer 23

AR = # of ppl sick / food substance