Outbreak investigation

Question 1

What is the definition of an outbreak?

Answer 1

More cases of a disease than expected in given area among a specific population over a given period of time

Question 2

Why investigate a disease outbreak?

Answer 2

Control - Prevention - Ascertain severity - Opportunity for research and training - Reassure public - Minimise disruption - Make recommendations

Question 3

What are the eight steps of a systematic approach to investigating a disease outbreak?

Answer 3

1 - confirm existence
2 - establish diagnosis
3 - determine magnitude
4 - analyse: who? where? when?
5 - working hypothesis
6 - test hypothesis
7 - further data collection and analysis
8 - communicate findings

Question 4

When analysing what do you do for the who, where and when?

Answer 4

Animal pattern = who
Spacial pattern = where
Temporal pattern = when

Question 5

What two methods can be used to plot the temporal pattern of disease outbreak more clearly?

Answer 5

Timeline of events - Epidemic curve

Question 6

What is the basic reproduction number? (Ro)

Answer 6

Average number of new cases caused by 1 infective individual in entirely susceptible population

Question 7

What does the Ro depend on? How can this be stopped?

Answer 7

Contact rate (rmovement restrictions) - Infectiousness (culling) - Susceptibility (vaccine)

Question 8

What value of Ro means that an outbreak is controlled?

Answer 8

Ro < 1