Outbreak Investigation Dr Ghazi Sharkas Jordan FETP (2009-2011)

How outbreaks are recognized The occurrence of an unusual disease, or an unusual number of cases of a disease By revision of the ordinary surveillance data By the patients or their relatives Rumors Some outbreaks are recognized through newspapers, television news, or Police departments

Why to investigate an outbreak Uncover a much more serious public health problem Identify risk factors associated with infection under study, that can be preventable

Why to investigate an outbreak Cont… Increasing knowledge of disease: Help Preventing future outbreaks Provide a base line for research about the disease under investigation Opportunities for training of health staff on problem investigation and rapid response

What to do after outbreak detection Epidemiological investigation Environmental investigations Interaction with the public, the media and sometimes the legal authorities

Epidemiological outbreak investigation steps

1. Confirm the existence of the outbreak Compare with Baseline surveillance data Data from local sources, neighboring areas or national data lab diagnosis of the pathogen Apply immediate control measures if the source is obviously defined

2. Verify the diagnosis Rule out laboratory error Interview / examine case patients Review medical records

3. Prepare for field work Compose a team and distribute roles Put an action plan Take all required facilities Ice bags Necessary lab utensils Laptop Sample questionnaires Other supplies

4. State a case definition using Symptoms or lab results When (time frame) Who's affected (person) Where (place) Categorize case definition, suspected, probable, confirmed

5.Case identification and line listing Case finding according to case definition Collect data on case patients Arrange data into line listing

What to include in a line listing Components of case definition Case name Date of symptom onset Demographic variables(age, occupation) Relevant risk factors

Example of a line listing Name Age Gender Date and time of onset Symptom1 Abdominal pain Symptom2 Fever Symptom3 Diarrhea Adress Group event Outcome Ahmad 23 male 8/9/2010 2 pm yes no Hospitalization Fatima 15 female 7/9/2010 10 am i.v fluids Kamal 8 Omar 34 6/9/2010 ORS Layla 37 7 pm nothing

6.Perform descriptive epidemiology Characterize the cases by Time: epidemic curve, when become ill Place: spot map, where the infection acquired, address Person: who was infected, what cases have in common (tables)

Importance of descriptive epidemiology Describe clinical features of the illness Describe demographic characteristics of affected persons Identify population at risk Provide clues to etiology, and mode of transmission Guide interventions

7. Generate a hypothesis guided by: Literature review Information from previous outbreaks Nature of suspected pathogen Interviews with case patients Local health officials opinion

8. Test hypotheses Current hypotheses may give a clue to the source of the outbreak Compare with known facts Conduct further studies if required (retrospective cohort, case control)

Which study to conduct Retrospective cohort: Done for well defined relatively small population, every one is included, calculate and compare attack rates (relative risk) Case-control: Done for larger population, controls selection is crucial, calculate odds ratio

9. Implement control measures Take control measures as early as possible in order to: Eliminate the source Interrupt transmission Reduce susceptibility

9. Implement control measures Control measures are guided by the results of epidemiological investigation and sometimes environmental specimens Control measures should be carefully implemented and justified especially if closure of restaurants and institutions is included

10. Communicate findings Communicate findings through dissemination of summary investigation and recommendations for control to the public and the press Communication helps to: Document your findings Justify your recommendations and control measures Protect against legal issues

THANK YOU Jordan FETP 2009-2011