Outbreak Investigation

Outbreak Investigation


Outbreak investigation is a systematic steps in order to define if we already have a problem or not if yes we need to investigate the problem extent and causes and make proper intervention to stop the propagation of the outbreak and end up by reporting the full story of the problem with the recommendation to be an educational source to avoid the causes of this outbreak to happen again

Outbreak Investigation

Outbreak Investigation


Remember…Speed and Accuracy both are needed also many steps can be done together and proper control measures have to be applied immediately once the source and/or mode of transmission is identified


1. Verify the diagnosis; identify the agent


We need to develop a case definition first, what is the diagnosis, which agent is pathogen is responsible for those cases (Virus, bacteria…) what are the symptoms and the magnitude of the problem???


The ‘case definition’ is a method of distinguishing persons as “cases” or “non-cases” based on if or not they satisfy the identified criteria. A new case definition will be formed for each outbreak and includes a mixture of signs, symptoms, dates, locations, etc. A case definition can be changed as the outbreak progresses and more data is found.


 2. Confirm that an outbreak exists


After proper case definition you need to compare against the usual endemic rate for the same cases are you above that rate if your cases are more than the expected cases (endemic rate) so you have outbreak so proceed for the next steps


Case identification: must meet one of the following criteria:

  • If the number of cases of hospital acquired infections (HAIs) exceed the facility own endemic rates.
  • Where are more than two cases of HAIs with the same organisms linked to the same exposure at any given time or place within 3 days.
  • If there are more than 2 transferred patients to ICUs with the same hospital acquired infections at any given time.
  • If there are one or more deaths attributed to same HAIs at any given time and locations.
  •  If there is an occurrence of two or more cases of reportable infectious diseases linked to the same exposure at any given time or place.
  • If laboratory data shows two or more cases of:-
    • Multidrug resistant organism (MDRO) isolates 
    •  Tuberculosis
    • Influenza
    • Varicella


3. Search for additional cases.

Start systematic searching for any new case or old missed cases by view medical report closed and opened and encourage other health care workers (Physicians , nurses , laboratory staff…etc.)To report to you immediately once suspected a new case


4. Prepare a line listing and draw epidemic curve

 ‘Line list’ is an important tool in active outbreak management. It is a collecting data that are pertinent to the case and the outbreak as a whole. It is a database composed of both rows and columns.  Each individual row represents a case and each individual column represents descriptive factors or clinical details  

  Epidemic curve: that graph that the cases of a disease that occurred during an epidemic are plotted according to the time of onset of illness in the cases.

 Remember you need to characterize the cases by place, persons, and time


5.Form a tentative hypothesis.

Assessment of the data to establish general host elements and exposures in order to find out a tentative hypothesis based on best guess.

6.Establish introductory control methods.

Launch control actions based on what you know. (Hand hygiene, isolation, cohorting cases _ suspected or confirmed, etc.)    Check if you need external assistance e.g. external consultant, MOH, local public health representative, educational institutions…etc.


7.Test the hypothesis.

Several LTCF problems never influence this step. It might finish devoid of interference or control actions may make the problem to terminate. Appropriate epidemiologic research and external help is needed.

8.Clarify the control means.

Combine extra control measures based the findings or reinforce the pre-established control measures if not followed

9.Monitor plus assess the control measures.


Check if the implemented control measures are appropriately developed or not and evaluate the result of number of the new cases


10. Prepare and disseminate the final report.


Once the outbreak is controlled a detailed report has to be edited stating all actions and measures taken and the circumstances with result of the cases (cured, discharged, transferred, died) and this report has to be disseminated to all concerned authorities (keep the patient confidentiality)



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