Overview of Outbreak Investigations

Goals

The goals of this presentation are to: Provide a general overview of the

basic steps of disease outbreak investigations

Describe factors that may contribute to a decision to investigate

Outbreaks: The basics

Goals of an outbreak investigation: To identify the source of illness To guide public health intervention

Ways to recognize an outbreak: Routine surveillance activities Reports from clinicians and

laboratories Reports from affected individuals

Why investigate an outbreak?

Characterize a public health problem Identify preventable risk factors Provide new research insights into

disease Train health department staff in

methods of public health investigations and emergency response

Steps of an outbreak investigation

1. Verify the diagnosis and confirm the outbreak

2. Define a case and conduct case finding

3. Tabulate and orient data: time, place, person

4. Take immediate control measures

Steps of an outbreak investigation

5. Formulate and test hypothesis

6. Plan and execute additional

studies

7. Implement and evaluate control

measures

8. Communicate findings

Steps of an outbreak investigation

These steps may occursimultaneously or be repeated as new information is received.

Verify the diagnosis and confirm the outbreak

Confirm laboratory testing Rule out misdiagnoses or

laboratory error

Define a case and conduct case finding

Develop a specific case definition using: Symptoms or laboratory results Time period Location

Conduct surveillance using case definition Existing surveillance Active surveillance (e.g. review medical

records) Interview case-patients

Tabulate and orient data Create line listing Person

Who was infected? What do the cases have in common?

Place Where were they infected? May be useful to draw a map

Time When were they infected? Create an epidemic curve

Take immediate control measures

If an obvious source of the contamination is identified…institute control measures immediately!

Formulate and test hypothesis

Develop hypotheses literature reviews of previous

outbreaks interviews of several case-patients

Conduct an analytic study to test hypotheses Retrospective cohort study Case-control study

Plan and execute additional studies

Environmental sampling Collect appropriate samples Allow epidemiological data to guide

testing If analytic study results are conclusive,

don’t wait for positive samples before implementing prevention

Implement and evaluate control measures

Prevent further exposure and future outbreaks by eliminating or treating the source

Work with regulators, industry, and health educators to institute measures

Create mechanism to evaluate both short- and long-term success

Communicate findings

Identify a single member of the investigation team to interact with media and communicate progress and findings

Summarize investigation, make recommendations, and disseminate report to all participants

Conclusions The steps listed for an outbreak

investigation comprise a brief introduction and rough guide. Only by conducting investigations repeatedly over an entire career will public health professionals truly learn the methods of outbreak investigations.

Snow’s “shoe leather epidemiology” serves as a model of critical thinking and public health action.

Online resources Information for Public Health Professionals-

Investigating Foodborne Disease Outbreaks. Available online at: http://www.cdc.gov/foodborneoutbreaks/info_healthprofessional.htm

To conduct an online outbreak investigation, “Botulism in Argentina,” visit the CDC website at: http://www.phppo.cdc.gov/phtn/casestudies/computerbased/default.htm

To explore an historical outbreak investigation, visit the online UNC John Snow Case Study at: http://www.sph.unc.edu/courses/Course_support/Case_studies/John Snow

References

Michael Gregg. Field Epidemiology. 2nd edition. Oxford University Press, 2002.

Control of Communicable Disease in Man, 17th edition. Chin, J (ed). APHA, 2000.

Principles & Practice of Infectious Diseases, 5th edition. Mandell GL, Bennett JE, Dolin R (eds). Churchill Livingstone; 2000