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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