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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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goals
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
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
diagnosis in an outbreak
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
diagnosis in an outbreak5
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
diagnosis in an outbreak6
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
to investigate or not to investigate
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
to investigate or not to investigate8
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
to investigate or not to investigate9
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
to investigate or not to investigate10
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
case definitions
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
case definitions12
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
case definitions13
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
case definition
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
case definition15
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
case definition16
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
conclusion
Conclusion
  • Deciding whether to conduct an outbreak investigation requires an balance of disease reporting, correct diagnosis, background research, and good judgment.
references
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)