Slide 1 - North Carolina Center by fjhuangjun

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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
   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

   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 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 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
   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
              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
              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
              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
   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 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 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
   Example: Listeriosis outbreak
       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 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 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
   Deciding whether to conduct an
    outbreak investigation requires an
    balance of disease reporting, correct
    diagnosis, background research, and
    good judgment.
                   References
1. 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/mm502
   6a3.htm)
2. Dombrowski, Julie. Hepatitis A Among Men who have
   Sex with Men. 2002
   (http://www.epi.state.nc.us/epi/gcdc/pdf/HepatitisA.pdf)
3. 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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