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S4 Lec 20: Outbreak Investigation (not lectured)

Draby Dra. Moderes ------ ------

Definition of Outbreak Occurrence of more cases of disease thanexpected in a given area among a specific

group of people over a particular period of timeor

Two or more linked cases of the sameillness

Objectives of Outbreak InvestigationsTo determine the cause of theoutbreakTo control ongoing outbreaksTo prevent future outbreaksTo provide statutorily mandatedservices

To strengthen surveillance at locallevelTo advance knowledge about a diseaseTo provide training opportunities

Specific Demands when InvestigatingOutbreaks

Unexpected eventNeed to act quicklyNeed for rapid controlWork carried out in the field

Steps of an Outbreak InvestigationConfirm outbreak and diagnosis

Case definition and identificationDescriptive data collection and

analysisDevelop hypothesisAnalytical studies to test

hypothesesSpecial studiesImplementation of control measures

Communication, including outbreakreport

Case DefinitionStandard set of criteria for deciding if aperson should be classified as sufferingfrom the disease under investigation.Clinical criteria, restrictions of time, place,personSimple, practical, objectiveSensitivity versus specificity

Example.Patient older than 5 years with severedehydration or dying of acute watery diarrhea intown X between 1 June and 20 July 2006

Examples of Case Definition: Possible Patient with severe diarrhea

Probable Patient older than 5 years with

severe dehydration or dying of acute watery diarrhea in town xbetween 1 June and 20 July 2006

Confirmed Isolation of Vibrio cholerae from

stool of patient

Control the Source of PathogenRemove source of contaminationRemove persons from exposureInactivate / neutralize the pathogenIsolate and/or treat infected persons

Interrupt TransmissionInterrupt environmental sourcesControl vector transmissionImprove personal hygiene

Modify Host ResponseImmunize susceptibleUse prophylactic chemotherapy

At the EndPrepare written reportCommunicate public health messagesInfluence public health policyEvaluate performance

Cessation of an outbreak occurs when thereis:

- elimination of source of contamination- interruption of transmission- reduction/exhaustion of susceptible- modification of the effect of primary

pathogen

An investigator should have knowledge onthe following:

various types of etiologic agents and theresultant disease

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epidemiological characteristics of outbreaks associated with differentetiologic agents of resultant diseasesclinical symptoms of resultant diseasesenvironmental and food sanitationpracticessources of exposure which are vulnerableto contamination with an infectious orchemical agent

laboratory test available to determinecausative agentsread/search for additional data on studies,prevention and control

Coverage of Exam:

Poster making andguidelines (5pts)Outbreak (20 pts)NCD (25pts)CD (25pts)Screening Test (25pts)

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