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Outbreak Investigation


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  • 1. Dr D K Niranjan
  • 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.  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.  Common source epidemics  Single source or point source  Continuous or Multiple exposure Propagated epidemics  Person to person spread
  • 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.  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.  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.  Epidemiologist Clinician/paediatrician/ neonatologist Microbiologist Member of Hospital Infection Control Committee Staff from affected unit/ward Others depending on the need
  • 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.  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.  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.  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.  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. 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. • 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.  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.  Epidemiologic/clinical investigation Environmental investigation Laboratory investigation Veterinary or vector borne investigation Forensics/Law enforcement investigation
  • 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.  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. Prepare study protocol1. Primary question(s)2. Significance3. Design4. Subjects5. Variables6. Statistical issues● Conduct study● Analyze data● Interpret findings
  • 21.  Epidemiologic inference  Validity (internal and external)  Threats to validity Causal inference – Causal criteria – Causal models
  • 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.  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. Every outbreak in thehospitals is an opportunity to improve infection control programme. Lessons learnt should be used to prevent future outbreaks
  • 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.  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.  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.  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.  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. Thank You