Investigation Of An Outbreak


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Investigation Of An Outbreak

  1. 1. Investigation of an Outbreak<br />Dr. Khaled Dhaifullah Al Ghaidany<br />Consultant family physician <br />
  2. 2. Pattern of spread of infectious diseases <br />Epidemic: the occurrence of an unusually increased number of cases within limited time and the cases can be traced to a common source<br />Outbreak: localized small epidemic in a closed or confirmed community in camps, schools, ..etc<br />Pandemic: large expanding epidemic involving different adjacent countries e.g. Influenza<br />
  3. 3. Endemic: Constant presence of a disease in the locality e.g. Schistosomiasis in Egypt <br />Sporadic: Occurrence of scattered unrelated cases irregularly distributed in time, place, person e.g. poliomyelitis<br />Zoonosis: Infectious disease transmitted under natural condition from intermediate animal to man e.g. Brucellosis<br />
  4. 4. Epizootic: Epidemic or outbreak in animals e.g. anthrax<br />Enzootic: Endemic disease among animals e.g. brucellosis <br />Exzootic: imported disease of animals<br />
  5. 5. Steps of investigation<br />Verify the diagnosis<br />Establish the existence of an outbreak<br />Identify and count cases<br />Perform descriptive epidemiology<br />Develop hypothesis<br />Evaluate the hypothesis<br />Implement control and preventive measures<br />Communicate the findings<br />
  6. 6. Verify the diagnosis<br />To ensure that the problem has been properly diagnosed and to rule out laboratory errors.<br />Revision of clinical and lab. results <br />A case definition must be based on clinical criteria with restriction by time, place, and person<br />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 <br />
  7. 7. Establish the existence of an outbreak<br />Avoid pseudo-epidemics: <br />Sudden increase in a doctor’s awareness of a disease <br />Improvement of reporting system<br />Increased notification rate <br />A single case of botulism is considered as an outbreak needing investigation<br />
  8. 8. Identify and count cases<br />Once a case definition is developed, start case finding from all possible sources by active or passive methods<br />Take a history from each confirmed or suspected cases<br />Clinical examination may be conducted to detect minor or modified forms of the disease <br />Laboratory investigation may be needed<br />
  9. 9. Perform descriptive epidemiology<br />Time: <br />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)<br />Place:<br />Draw the spot map ( where cases live, work, or may be exposed). It may provide important etiologic clues.<br />Person:<br /> collect personal data (age, sex, marital status, occupation, leisure activity, use of medications, tobacco and drugs<br />
  10. 10. Develop hypothesis<br />From the revision of descriptive epidemiology a hypothesis can be generated. <br />It should address the following:<br />1- source of the agent<br />2- mode of transmission<br />3- the causative exposure<br />
  11. 11. Evaluate the hypothesis<br />It can be evaluated by comparing it with the established facts when clinical, laboratory, environmental, and/or epidemiological evidence obviously support it<br />If this is not the case, then analytic epidemiology is used to test the hypothesis through case control or cohort study.<br />Laboratory and environmental studies may be used to confirm the epidemiological findings<br />
  12. 12. Implement control and preventive measures<br /> Must be applied as soon as possible even if the source is not known yet.<br />Control measures are applied at the weak link in the chain of infection ( might be the agent, the host, or the reservoir)<br />Control measures: <br /><ul><li>Notification
  13. 13. Isolation
  14. 14. Quarantine </li>