Outbreak Investigation


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Outbreak Investigation

  1. 1. Dr D K Niranjan
  2. 2.  “A sudden rise in the incidence of a disease” The occurrence in a community or region of cases of an illness with a frequency clearly in excess of normal expectancy.
  3. 3.  Endemic infections in hospital  Usual or expected frequency of infections in the hospital (background rate) Epidemic nosocomial infections in hospital  Unusual occurrence of infections clearly in excess of expected occurrence (background rate)  Isolation of unusual (rare) organism  Isolation of organism with different anti-microbial susceptibility, or molecular typing
  4. 4.  Common source epidemics  Single source or point source  Continuous or Multiple exposure Propagated epidemics  Person to person spread
  5. 5.  Outbreak in Hospital/ Health facility Outbreak in Community Outbreak in community may have origin in a hospital Outbreak in community may trigger outbreak in hospital We take almost similar steps to investigate community and hospital outbreaks Infection control programme in hospital may not only prevent outbreak in hospital, but in community also
  6. 6.  Prevent additional cases in the current outbreak Prevent future outbreaks Learn about a new disease Learn something new about an old disease Reassure the public Minimize economic and social disruption Teach epidemiology
  7. 7.  Magnitude Characterization of cases by time, person and place Risk factors Source of infection, mode of transmission Control of outbreak Prevent recurrence Document the outbreak – lessons learnt
  8. 8.  Epidemiologist Clinician/paediatrician/ neonatologist Microbiologist Member of Hospital Infection Control Committee Staff from affected unit/ward Others depending on the need
  9. 9.  Confirm the diagnosis Confirm the existence of an outbreak Define at-risk population and characterize the cases by time, person and place (Case definition; case ascertainment – identify and count cases; line list of cases; epidemic curve) Review of literature about outbreaks/isolates Formulate hypothesis about genesis of outbreak (source and route of infection) Make further investigations to confirm/refute the hypothesis (case control studies, culture surveys) Control the outbreak Prepare and disseminate the report (documentation)
  10. 10.  Case definition changed Introduction of new laboratory tests Frequency of testing of patients changed Introduction of a new medical or surgical procedure New areas or population included under the surveillance
  11. 11.  Confirm outbreak  – Confirm diagnoses  – Case definition  – Case line listing started  – Case finding  – Case interviews  – Complete line listing  – Case descriptive epidemiology  – Establish baseline occurrence of cases  – Rule out alternative explanations (chance, bias, ...) Generate preliminary causal hypotheses
  12. 12.  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 characteristics Specific inclusion and exclusion criteria Simple, practical, objective Suspect, probable, confirmed Case definition may be more sensitive initially Case definition should be more specific when sufficient information is available
  13. 13.  Identification No. Age Sex Date of admission Cause of admission Intervention/surgery/procedure done, device used, if any Date of undertaking intervention/surgery/procedure Place where intervention/surgery/procedure undertaken Date of onset of outbreak associated clinical features Outbreak associated clinical features Lab investigations Result of lab investigations Diagnosis (Nosocomial infection) Outcome: Still ill, recovered, died, other (specify) Other relevant variables Comments
  14. 14. Point source 25 20 15 10 5 0 1 3 5 7 9 11 13 15 17 19 Multiple curves Continuous source20 2015 1510 105 50 0 1 3 5 7 9 11 13 15 17 19 1 4 7 10 13 16 19
  15. 15. • 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
  16. 16.  Systematically review known causal factors (Transmission mechanisms and dynamics) Prioritize likely causes to guide control measures (Step 3) Generate testable hypotheses to conduct analytic study (Step 4) if cause remains unknown or control measure not working
  17. 17.  Epidemiologic/clinical investigation Environmental investigation Laboratory investigation Veterinary or vector borne investigation Forensics/Law enforcement investigation
  18. 18. Implement control measures May occur at any time during the outbreak!!Control the source of infection Interrupt transmission Modify host response Prevent recurrence
  19. 19.  Control measures related to source of infection  Identify and remove the source of infection  Isolation of cases  Quarantine of healthy contacts of infectious disease Interrupt transmission Protect susceptible host  Immunization  Chemoprophylaxis Non specific measures  Surveillance programme for detection/control of infections  Risk communication (IEC)  Research
  20. 20. Prepare study protocol1. Primary question(s)2. Significance3. Design4. Subjects5. Variables6. Statistical issues● Conduct study● Analyze data● Interpret findings
  21. 21.  Epidemiologic inference  Validity (internal and external)  Threats to validity Causal inference – Causal criteria – Causal models
  22. 22.  Detect outbreaks Detect public health threats Detect infectious cases (case finding) Monitor trends in a target population Monitor exposed individuals for symptoms Monitor treated individuals for complications Direct public health interventions Evaluate public health interventions Generate hypotheses for further evaluation
  23. 23.  Communicate preliminary assessments and recommendations (letter, memo) Prepare interim/final reports Prepare manuscript (optional) Risk communication strategy (what to say) Media communication strategy (how to say it)
  24. 24. Every outbreak in thehospitals is an opportunity to improve infection control programme. Lessons learnt should be used to prevent future outbreaks
  25. 25.  Assign a spokesperson who has the authority, is knowledgeable and respected by community, health professionals and media Give clear, accurate and timely information. Avoid technical terms, if possible. Update information regularly. Forward 3 positive points against one negative point. Do not allow media to control the entire dialogue Be frank about your efforts and the challenges
  26. 26.  Chronology of events - How was the outbreak suspected? Methodology adopted for investigation  Outbreak investigation Team  Case definition  Case ascertainment  Lab investigations Epidemiological observations  Characterization of cases/deaths by time, person and place Results of laboratory investigations Analysis and interpretation of data collected and compiled Further investigations undertaken Conclusion about source and route of infection Interventions made/recommended Dissemination of report including executive summary to all stakeholders
  27. 27.  Viral hepatitis B outbreaks occurred in hospitals in 1980s and 90s  In 1997, NICD investigated 3 community outbreaks of viral hepatitis B  Mehasana district in Gujarat  Sirsa district in Haryana  Sri Ganganagar in Rajasthan  Inadequately sterilized needles and syringes resulted in these outbreaks  Inadequate sterilization still causes many infectious diseases outbreaks in hospitalsSource: WHO 1998; 76:93-98; Epidemiol Infect 2000;125:367-375
  28. 28.  ESI Hospital Colony, Madurai had an explosive outbreak of chikungunya in September 2009 Chikungunya cases were admitted to the ESI Hospital There was heavy breeding of Aedes mosquitoes in the campus Infection was transmitted to other cases and hospital staff 9 of 11 doctors and 34 of 37 nurses who worked in the hospital or stayed in the campus were affected during the outbreak Most of other residents of the hospital colony were also affected Hospital transmission of dengue and chikungunya has been observed in other cities also in the past
  29. 29.  A patient admitted in a hospital probably started the outbreak  Infection spread to other patients, visitors and health acre workers  66 probable cases, 45 died  Many including health care workers got infection in the hospital  No exposure of cases to animals  Human to human transmission of Nipah/ Hendra virus was suspectedSource: IJMR 2006;123: 553-560
  30. 30. Thank You
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