Overview of Outbreak Investigations

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Overview of Outbreak Investigations
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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

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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

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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

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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

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Steps of an outbreak investigation

• Formulate and test hypothesis
• Plan and execute additional studies
• Implement and evaluate control measures
• Communicate findings

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Steps of an outbreak investigation

• These steps may occur
• simultaneously or be repeated as
• new information is received.

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Verify the diagnosis and confirm the outbreak

• Confirm laboratory testing
• Rule out misdiagnoses or laboratory error

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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

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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

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Take immediate control measures

• If an obvious source of the contamination is
  identifiedinstitute control measures immediately!

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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

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Plan and execute additional studies

• Environmental sampling
• Collect appropriate samples
• Allow epidemiological data to guide testing
• If analytic study results are conclusive, dont
  wait for positive samples before implementing
  prevention

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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

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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

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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.
• Snows shoe leather epidemiology serves as a
  model of critical thinking and public health
  action.

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Online resources

• Information for Public Health Professionals-
  Investigating Foodborne Disease Outbreaks.
  Available online at
• http//www.cdc.gov/foodborneoutbreaks/info_health
  professional.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

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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