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Overview of Outbreak Investigations

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  1. Overview of Outbreak Investigations

  2. 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

  3. 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

  4. 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

  5. Steps of an outbreak investigation • Verify the diagnosis and confirm the outbreak • Define a case and conduct case finding • Tabulate and orient data: time, place, person • Take immediate control measures

  6. Steps of an outbreak investigation • Formulate and test hypothesis • Plan and execute additional studies • Implement and evaluate control measures • Communicate findings

  7. Steps of an outbreak investigation These steps may occur simultaneously or be repeated as new information is received.

  8. Verify the diagnosis and confirm the outbreak • Confirm laboratory testing • Rule out misdiagnoses or laboratory error

  9. 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

  10. 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

  11. Take immediate control measures • If an obvious source of the contamination is identified…institute control measures immediately!

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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