Principles of Outbreak Investigation

Dr MalimuDepartment of Epidemiology & Biostatistics

Learning Objectives

When you have completed this session you will be able to:

♦ Define the terms “cluster”, “outbreak”, and “epidemic”

♦ List the objectives of an outbreak investigation

♦ List the steps of an outbreak investigation

Definitions

♦ Outbreak– Occurrence of more cases of disease than

expected in a given area or among a specific group of people over a particular period of time

♦ Epidemic– Used interchangeably with outbreak

Definitions

♦ Cluster– Group of cases in specific time and place that

may or may not be greater than the expected rate

– Aim of investigating cluster is to determine the baseline rate of disease for that time and place

Detecting Outbreaks

♦ Routine analysis of surveillance data♦ Reports from community♦ Report from an alert clinician♦ Local newspapers♦ Others

Objectives of an Outbreak - 1

♦ Institute control and prevention measures– If cases are occurring, prevent new cases

• Assess extent of outbreak• Size and characteristics of pop at risk

– If outbreak is almost over, further investigate• Identify factors contributing to outbreak

Control vs further investigation

Knowncausative agent

UnknownCausativeagent

Investigation +Control +++

Investigation+++Control +

Investigation+++Control +++

Investigation+++Control+

Source/Mode of Transmission

Known Unknown

Objectives of an Outbreak - 2

♦ Research opportunities– Gain additional knowledge

• Study natural history of disease• Assess impact of control measures• Usefulness of new epi and lab technique

♦ Training– Improve skills of logical thinking,

epidemiologic know-how and judgement, problem solving ability

Objectives of an Outbreak - 3

♦ Severity and risk to others

♦ Public, political, or legal concerns– May override scientific concerns to investigate

♦ Programme consideration– Investigate to evaluate effectiveness of

programme

Steps of an Outbreak Investigation

♦ Establish the existence of an outbreak♦ Verify the diagnosis♦ Define a case and count cases♦ Orient the data in terms of time ,place and person♦ Determine who is at risk of becoming ill♦ Develop a hypothesis♦ Compare hypothesis with established facts♦ Plan a more systematic study♦ Prepare a written report♦ Execute control and prevention measures

Recap

Now that you have completed this session you should be able to:

♦ Define the terms “cluster”, “outbreak”, and “epidemic”

♦ List the objectives of an outbreak investigation

♦ List the steps of an outbreak investigation

♦ Definition♦ Causative agent♦ Epidemilogy –prevalence, globally,Africa,EA ,Tanzania.♦ Lifecycle♦ Signs and symptoms♦ Lab test♦ Treatment♦ Control and prevention♦ Public health importance