Principles of Outbreak Management WHOCSR Definition of outbreak
Principles of Outbreak Management WHO/CSR
Definition of outbreak • Occurrence of more cases of disease than expected in a given area among a specific group of people over a particular period of time or • Two or more linked cases of the same illness WHO/CSR
Objectives of outbreak investigations • To control continuing outbreaks • To prevent future outbreaks • To provide statutorily mandated services • To strengthen surveillance at local level • To advance knowledge about a disease • To provide training opportunities WHO/CSR
Specific demands when investigating outbreaks • Unexpected event • Need to act quickly • Need for rapid control • Work carried out in the field Systematic approach WHO/CSR
Steps of an outbreak investigation • • Confirm outbreak and diagnosis Case definition and identification Descriptive data collection and analysis Develop hypothesis Analytical studies to test hypotheses Special studies Implementation of control measures Communication, including outbreak report WHO/CSR
Detection Routine surveillance Clinical / Laboratory General public Media Is this an outbreak? Diagnosis verified ? clinical + laboratory Link between cases? Expected numbers? WHO/CSR
Sequence of Events in outbreak detection and confirmation (I) Primary 1 st case Case at HC Report Samples Lab to DMO taken result CASES Response begins Opportunity for control DAY WHO/CSR
Sequence of events in outbreak detection and confirmation (II) Response PRIM HC REP SAMP RES begins Potential Cases Prevented CASES DAY WHO/CSR
Outbreak confirmed Immediate control measures? Further investigation? WHO/CSR
Outbreak confirmed Immediate control measures? Prophylaxis Exclusion / isolation Public warning Hygienic measures Further investigation? Unknown aetiology (pathogen/source/transmission) Cases serious Cases still occurring Public pressure Training opportunity Scientific interest Assistance ? WHO/CSR
Epidemiologist Microbiologist Environmental specialist Ministry / Government Press officer Others Outbreak Investigation Team? FIELD WHO/CSR
Investigation Vector Reservoir Surveillance Dead Sick Prediction Exposed Clinicians Epidemiology Coordination Education Health personnel Special groups General population Laboratory Clinical Diagnostic Media Authorities Specimen transfer Decisions Infrastructure Regulations Vaccinations etc WHO/CSR
Epidemiologist Microbiologist Environmental specialist Ministry / Government Press officer Others Outbreak Investigation Team? Assess situation Examine available information Preliminary hypothesis ? Case definition Case finding Descriptive epidemiology WHO/CSR
Case definition • Standard set of criteria for deciding if a person should be classified as suffering from the disease under investigation. • Clinical criteria, restrictions of time, place, person • Simple, practical, objective • Sensitivity versus specificity WHO/CSR
Case definition: example Patient older than 5 years with severe dehydration or dying of acute watery diarrhoea in town “x” between 1 June and 20 July 1998 WHO/CSR
Case definition: categorisation • Possible – Patient with severe diarrhoea • Probable – Patient older than 5 years with severe dehydration or dying of acute watery diarrhoea in town “x” between 1 June and 20 July 1998 • Confirmed – Isolation of Vibrio cholerae from stool of patient WHO/CSR
Identify & count cases Clearly identifiable groups Hospitals Laboratories Schools Workplace, etc Obtain information Perform descriptive epidemiology WHO/CSR
Identify & count cases Obtain information Identifying information Demographic information Clinical details Risk factors Perform descriptive epidemiology WHO/CSR
Identify & count cases Obtain information Perform descriptive epidemiology Orient cases in - time - place - person WHO/CSR
Cases Time Person Place Evaluate information Pathogen? Source? WHO/CSR Transmission?
Cases of viral meningitis by date of admission (n=416) Cyprus, 5 July - 5 November 5 1996 WHO/CSR
Point source Examples of epidemic curves Continuing common source Multiple waves -person to person or further outbreak WHO/CSR
Admissions per 100, 000 population for viral meningitis by age group. Cyprus, 5 July - 5 November 1996 WHO/CSR
Admissions per 100, 000 population for viral meningitis by district; Cyprus, 5 July - 5 November 1996 Nicosia Paphos F. Famagusta Larnaca Limassol Cases per 100, 000 1 -49 50 -99 100 + No data WHO/CSR
WHO/CSR
Develop hypotheses • Who is at risk of becoming ill? • What is the disease causing the outbreak? • What is the source and the vehicle? • What is the mode of transmission? Compare hypotheses with facts WHO/CSR
Test specific hypotheses Analytical epidemiological studies Cohort Case-control WHO/CSR
Implement control measures May occur at any time during the outbreak!! Control the source of the pathogen Interrupt transmission Modify host response Prevent recurrence WHO/CSR
Control the source of pathogen • Remove source of contamination • Remove persons from exposure • Inactivate / neutralise the pathogen • Isolate and/or treat infected persons WHO/CSR
Interrupt transmission • Interrupt environmental sources • Control vector transmission • Improve personal sanitation WHO/CSR
Modify host response • Immunise susceptibles • Use prophylactic chemotherapy WHO/CSR
Source/Transmission unknown Investigation +++ Control +++ Control + Aetiology known WHO/CSR Source: Goodman 1990
At the end • Prepare written report • Communicate public health messages • Influence public health policy • Evaluate performance WHO/CSR
Thank you WHO/CSR
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