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Embarking on an Outbreak Investigation

Embarking on an Outbreak Investigation. Goals . The goals of this presentation are to discuss: The importance of verifying case reports Methods to determine if an outbreak investigation is necessary Creating and using case definitions. Verify the Diagnosis.

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Embarking on an Outbreak Investigation

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  1. Embarking on an Outbreak Investigation

  2. Goals • The goals of this presentation are to discuss: • The importance of verifying case reports • Methods to determine if an outbreak investigation is necessary • Creating and using case definitions

  3. Verify the Diagnosis • Before launching a full investigation, verify: • Signs • Symptoms • Test results • Ways to reduce diagnosis error • Confirm appropriate lab tests were performed • Confirm symptoms were reported accurately • For rare conditions, educate clinicians

  4. Diagnosis in an Outbreak • Patients may present with a known/highly suspected agent • Verify with standard lab test • Not every case needs to be lab-confirmed • Example: Listeriosis

  5. Diagnosis in an Outbreak • Patient may present with an unknown agent but with characteristic symptoms • Identify probable agent based on: • Signs and symptoms • Age of patients, season, incubation period • Lab results • Example: gastrointestinal illness • No outbreak exists if cases result from different agents

  6. Diagnosis in an Outbreak • If cases have a common link or are the same illness, you can investigate without knowing the agent • If cases do not appear to be related or share a common exposure, you may not want to proceed with an investigation

  7. To Investigate or not to Investigate • Consider the following factors when deciding whether or not to investigate an outbreak • It could be “true” outbreak with common cause • It could be unrelated cases of the same disease • Severity of illness • Transmissibility • Local politics • Public concern • Available resources

  8. To Investigate or not to Investigate • Key deciding factor is often if there are unusually high numbers of cases • “Unusually high”=more cases than expected • This depends on the disease: • Multiple cases of respiratory illness in grade school during winter may be usual • Single case of botulism or anthrax is more than expected

  9. To Investigate or not to Investigate • How do you determine if you have more cases than expected? • For notifiable diseases • Cases are reported to health department • Compare number of current reports with previous weeks • Compare number of current reports with same time period or season in previous years

  10. To Investigate or not to Investigate • How do you determine if you have more cases than expected? • For non-notifiable conditions: • Check hospital discharge records, mortality data, cancer registries, birth defect registries or other available records • Use data from neighboring areas • Call local health care providers • Call community members

  11. Case Definitions • A case definition • Allows a simple, uniform way to identify cases • “Standardizes” the investigation • Is unique to outbreak but is based on objective criteria

  12. Case Definitions • Always includes: Person, Place and Time • Person: relevant information about personal characteristics • Place: information about where the exposure is thought to have occurred • Time: dates during which exposure was thought to have occurred

  13. Case Definitions • Can emphasize sensitivity or specificity in case definition • Usually emphasize sensitivity early in investigation • Can narrow case definition as more information is obtained

  14. Case Definition • Example: Listeriosisoutbreak • Person: mother of a stillborn or premature infant infected with Listeria or a pregnant woman/mother with febrile illness • Place: lived in Winston-Salem, North Carolina • Time: October 24, 2000-January 1, 2001

  15. Case Definition • Example: Salmonellosis outbreak • Person: Has culture-confirmed Salmonella enteriditis, is a North Carolina resident • Place: North Carolina • Time: July 1, 2001-September 1, 2001

  16. Case Definition • Categories of cases • Confirmed • Symptoms characteristic of the agent • Lab test • Epidemiologic link • Probable • Symptoms confirmed • No lab or epidemiologic link • Suspected • Symptoms reported but not confirmed • No lab or epidemiologic link

  17. Conclusion • Deciding whether to conduct an outbreak investigation requires an balance of disease reporting, correct diagnosis, background research, and good judgment.

  18. References • Centers for Disease Control. Outbreak of Listeriosis Associated with Homemade Mexican-Style Cheese – North Carolina, October 2000 – January 2001. MMWR July 6, 2001; 50 (26):560-2. (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5026a3.htm) • Dombrowski, Julie. Hepatitis A Among Men who have Sex with Men. 2002 (http://www.epi.state.nc.us/epi/gcdc/pdf/HepatitisA.pdf) • Dicker RC, et al. Investigating an Outbreak. In: Principles of Epidemiology: An Introduction to Applied Epidemiology and Biostatistics. Centers for Disease Control and Prevention, 1992: 347-350. (http://www.phppo.cdc.gov/PHTN//catalog/pdf-file/Epi_Course.pdf)

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