Investigation Of An Outbreak
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Investigation Of An Outbreak






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Investigation Of An Outbreak Investigation Of An Outbreak Presentation Transcript

  • Investigation of an Outbreak
    Dr. Khaled Dhaifullah Al Ghaidany
    Consultant family physician
  • Pattern of spread of infectious diseases
    Epidemic: the occurrence of an unusually increased number of cases within limited time and the cases can be traced to a common source
    Outbreak: localized small epidemic in a closed or confirmed community in camps, schools, ..etc
    Pandemic: large expanding epidemic involving different adjacent countries e.g. Influenza
  • Endemic: Constant presence of a disease in the locality e.g. Schistosomiasis in Egypt
    Sporadic: Occurrence of scattered unrelated cases irregularly distributed in time, place, person e.g. poliomyelitis
    Zoonosis: Infectious disease transmitted under natural condition from intermediate animal to man e.g. Brucellosis
  • Epizootic: Epidemic or outbreak in animals e.g. anthrax
    Enzootic: Endemic disease among animals e.g. brucellosis
    Exzootic: imported disease of animals
  • Steps of investigation
    Verify the diagnosis
    Establish the existence of an outbreak
    Identify and count cases
    Perform descriptive epidemiology
    Develop hypothesis
    Evaluate the hypothesis
    Implement control and preventive measures
    Communicate the findings
  • Verify the diagnosis
    To ensure that the problem has been properly diagnosed and to rule out laboratory errors.
    Revision of clinical and lab. results
    A case definition must be based on clinical criteria with restriction by time, place, and person
    A doctor called to an “outbreak of food poisoning” is unwise to begin by collecting information about recent meals before confirming that the clinical history is compatible with the diagnosis
  • Establish the existence of an outbreak
    Avoid pseudo-epidemics:
    Sudden increase in a doctor’s awareness of a disease
    Improvement of reporting system
    Increased notification rate
    A single case of botulism is considered as an outbreak needing investigation
  • Identify and count cases
    Once a case definition is developed, start case finding from all possible sources by active or passive methods
    Take a history from each confirmed or suspected cases
    Clinical examination may be conducted to detect minor or modified forms of the disease
    Laboratory investigation may be needed
  • Perform descriptive epidemiology
    Draw epidemic curve (histogram: No. of cases by their date of onset) to identify the date of exposure to the source of infection, and the epidemic pattern (e.g. common source or propagated)
    Draw the spot map ( where cases live, work, or may be exposed). It may provide important etiologic clues.
    collect personal data (age, sex, marital status, occupation, leisure activity, use of medications, tobacco and drugs
  • Develop hypothesis
    From the revision of descriptive epidemiology a hypothesis can be generated.
    It should address the following:
    1- source of the agent
    2- mode of transmission
    3- the causative exposure
  • Evaluate the hypothesis
    It can be evaluated by comparing it with the established facts when clinical, laboratory, environmental, and/or epidemiological evidence obviously support it
    If this is not the case, then analytic epidemiology is used to test the hypothesis through case control or cohort study.
    Laboratory and environmental studies may be used to confirm the epidemiological findings
  • Implement control and preventive measures
    Must be applied as soon as possible even if the source is not known yet.
    Control measures are applied at the weak link in the chain of infection ( might be the agent, the host, or the reservoir)
    Control measures:
    • Notification
    • Isolation
    • Quarantine