This document outlines the steps for investigating an outbreak of infectious disease: 1. Verify the diagnosis and define cases. Develop a case definition based on clinical criteria. 2. Establish that an outbreak exists by determining if cases exceed normal levels. Avoid pseudo-outbreaks from improved reporting. 3. Identify and count cases through active and passive surveillance. Take histories and examine all confirmed and suspected cases. 4. Perform descriptive epidemiology including time, place, and person analyses to generate hypotheses about the source and transmission of the disease. 5. Implement control measures as soon as possible before confirming the source to break the chain of infection. Measures include notification, isolation, and quarantine.

1. Investigation of an Outbreak Dr. Khaled Dhaifullah Al Ghaidany Consultant family physician

2. 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

3. 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

4. Epizootic: Epidemic or outbreak in animals e.g. anthrax Enzootic: Endemic disease among animals e.g. brucellosis Exzootic: imported disease of animals

5. 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

6. 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

7. 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

8. 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

9. Perform descriptive epidemiology Time: 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) Place: Draw the spot map ( where cases live, work, or may be exposed). It may provide important etiologic clues. Person: collect personal data (age, sex, marital status, occupation, leisure activity, use of medications, tobacco and drugs

10. 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

11. 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

13. Isolation

14. Quarantine