13: Outbreak Investigation

Question 1

What is an outbreak?

What is a cluster?

What is an endemic, epidemic?

Answer 1

Outbreak
occurence of more than expected cases (epidemic limited to localized increase in incidence)

Cluster
aggregation of cases in a given area over a particular period, its not important if the number of cases is ore than expected

Endemic
habitual presence of a disease within a given geographic area

Epidemic
the occurence of more cases of disease than expected in a given area or among a specific population over a particular time period, linked to outbreak

Pandemic
Wordwide spread of disease

Question 2

First 5 steps in outbreak investigation

Answer 2

1. Prepare for field work
scientific, investigative, management and operational issues must be adressed

2. Establish the outbreak existence
Surveillance system, hospital discharge records, mortality stats, registries, telephone survey

3. Verifiy diagnosis
Ensure that disease is identified properly, not due to an lab error

4. Construct a working case definition
Standard set of criteria for deciding wheter an individual should be classified as a case (clinic, lab criteria, restriction by time, place and person)

5. Find cases and record infos
Passive (asking for reports) or active (visit facilities) surveillance

• ID, demographic, clinical infos, risk factors, reporter information

Question 3

6th step of outbreak investigation

Answer 3

6. Perform descriptive epidemiology
epidemic curves, disease mapping

Question 4

7th step of outbreak investigating

Answer 4

7. Develop hypothesis
Source of agent, mode of transmission, exposure causing disease

• what you know about disease, talk to case-patients, descriptive empidemiology, outliers

Question 5

8th, 9th and 10th step in outbreak investigation

Answer 5

8. Evaluate hypothesis epidemiologically
Analysis via:
- cohort studies (relative risk, population attributable risk)
- Case-control studies (Odds ratio)
- Statistical testing (Chi^2)

9. If necessary, rethink your hypothesis:
- consider new vehicles, modes

10. Compare and reconcile with other studies

Question 6

11th step of outbreak investigation

Answer 6

11. Implement prevention measures
primary goal is to prevent further outbreak, therefore implement control measures directed against 1 or more segments in the chain of transmission (agent, source, mode of transmission, host)

Question 7

12th and 13th step of outbreak investigation

Answer 7

12. Initiate or maintain surveillance
monitor prevention measures, they need to work, is number slowing down, where do new cases occur?

13. Communicate findings
Summmarize investigation, findings outcomes during and when its concluded