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Outbreak investigation steps under IDSP program
Outbreak investigation steps under IDSP program
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Outbreak investigation steps under IDSP program
- 1. Outbreak investigation, response andcontrol Integrated Disease Surveillance Programme (IDSP) district surveillance officers (DSO) course
- 2. 2 Preliminary questions tothe group • What is your experience in outbreak investigations? • If yes, what difficulties did you face? • What would you like to learn about outbreak investigations?
- 3. 3 Outline of thesession 1. Outbreaks and epidemics 2. Outbreak detection 3. Outbreak investigation 4. Managerial aspects of outbreak investigations
- 4. 4 Endemic versus epidemic •Endemicity Disease occurring in a population regularly at a usual level • Tuberculosis, Malaria • Epidemics Unusual occurrence of the disease in excess of its normal expectation • In a geographical location • At a given point of time e.g. Hepatitis E, measles, cholera Outbreaks
- 5. 5 Outbreaks versus epidemics •Occurrence of cases of an illness in excess of expected numbers • Scale Outbreak • Limited to a small area, within one district or few blocks Epidemic • Covers larger geographic areas • Linked to control measures in district/state No exact precise threshold: Use a word or the other according to whether you want to generate or deflect attention • Be aware of legal implications of the use of the term “Epidemic” in India (Epidemic disease act, being revised) Outbreaks
- 6. 6 Sources of information todetect outbreaks • Event-based surveillance Rumour register • To be kept in standardized format in each institution • Rumours need to be investigated Community informants • Private and public sector Media • Important source of information, not to neglect • Case-based surveillance Review of routine surveillance data and triggers Detection
- 7. 7 Early warning signalsfor an outbreak • Clustering of cases or deaths • Increases in cases or deaths • Single case of disease of epidemic potential • Acute febrile illness of an unknown etiology • Two or more linked cases of disease with outbreak potential (e.g., Measles, Cholera, Dengue, Japanese encephalitis or plague) • Unusual isolate (Cholera O 139) • Shifting in age distribution of cases (Cholera O 139) • High vector density • Natural disasters Detection
- 8. 8 Importance of timelyaction: The first information report (Form C) • Filled by the reporting unit • Submitted to the District Surveillance Officer as soon as the suspected outbreak is verified • Sent by the fastest route of information available Telephone Fax E-mail Detection
- 9. 9 The rapid responseteam • Composition Epidemiologist, clinician and microbiologist • Entomologist when vector-borne disease Gathered on ad hoc basis when needed • Role Confirm and investigate outbreaks • Responsibility Assist in the investigation and response Primary responsibility rests with local health staff Detection
- 10. 10 Objectives of anoutbreak investigation 1. Verify 2. Recognize the magnitude 3. Diagnose the agent 4. Identify the source and mode of transmission 5. Formulate prevention and control measures Host Environment Agent An outbreak comes from a change in the way the host, the environment and the agent interact: This interaction needs to be understood to propose recommendations Investigations
- 11. 11 The balance betweeninvestigation and control while responding to an outbreak Source / transmission Known Unknown Etiology Known Control +++ Investigate + Control + Investigate +++ Unknown Control +++ Investigate +++ Control + Investigate +++ Investigations
- 12. 12 Steps in outbreakresponse 1. Verifying the outbreak 2. Sending the rapid response team 3. Monitoring the situation 4. Declaring the outbreak over 5. Reviewing the final report Investigations
- 13. 13 Step 1: Verifyingthe outbreak • Validate the source of information ? Change in the reporting system ? Change in the population size ? Acute reporting of old, chronic cases • Check with the concerned medical officer: ? Abnormal increase in the number of cases ? Clustering of cases ? Epidemiological link between cases ? Triggering event ? Deaths Investigations
- 14. 14 Step 2: Sendingthe rapid response team • Review if the source and mode of transmission are known • If not, constitute team with: Medical officer Epidemiologist Laboratory specialist • Formulation of hypothesis on basis of the description by time, place and person (Descriptive epidemiology) ? Does the hypothesis fits the fact YES: Propose control measures NO: Conduct analytical studies Investigations
- 15. 15 Yes -> Control measures Hypothesisfit the facts: -> Control measures Hypothesis does not fit the facts: -> Analytical investigations Time, place person description Formulation of hypothesis No -> Clinical, microbiological and epidemiological investigation Yes -> Are the source and modes of transmission known? No Unusual event: Is this an outbreak? Investigating an outbreak
- 16. 16 Example: Outbreak ofacute hepatitis (E) in Baripada, Orissa, 2003 • Identification of a cluster of acute hepatitis cases • Diagnosis: HEV infection • Use time, place and person analysis of surveillance data to suggests hypotheses
- 17. 17 0 5 10 15 20 25 30 35 40 45 1/1/04 1/3/04 1/5/04 1/7/04 1/9/04 1/11/04 1/13/04 1/15/04 1/17/04 1/19/04 1/21/04 1/23/04 1/25/04 1/27/04 1/29/04 1/31/04 2/2/04 2/4/04 2/6/04 2/8/04 2/10/04 2/12/04 2/14/04 2/16/04 2/18/04 2/20/04 2/22/04 2/24/04 2/26/04 2/28/04 3/1/04 3/3/04 3/5/04 3/7/04 Number of cases and deaths Cases Deaths Investigation started Strike among municipal Workers: Water treatmentstopped Cases of acute hepatitis (E) by date of onset, Baripada, January-March 2004 Time: A cluster a month after a strike in the water treatment centre Investigations
- 18. 18 Chip at rive r Attack rate ofacute hepatitis (E) by residence, Baripada, Orissa, India, 2004 0 - 0.9 / 1000 1 - 9.9 / 1000 10 -19.9 / 1000 20+ / 1000 Attack rate Underground water supply Pump from river bed Place: Highest rates next to the pump taking water from river bed Investigations
- 19. 19 Attack rate ofacute hepatitis (E) by age and sex, Baripada, Orissa, India, 2004 Cases Population Attack rate per 1000 Age 0-4 1 1012 0.1 5-9 11 21802 2 10-14 37 74004 5 15-44 416 51358 81 45+ 73 56153 13 Sex Male 341 102683 3.3 Female 197 101646 1.9 rson: Attack rate compatible with HEV Investigations
- 20. 20 What hypotheses wouldyou generate for the outbreak of acute hepatitis (E) in Baripada, Orissa, 2003? • Time: It happens a month after a strike in the water treatment plant • Place: It is clustered around a water source that takes water from the river • Person: Adults are mostly affected The river water may have been supplied untreated in the area of the outbreak because of the strike at the water treatment plant
- 21. 21 Descriptive versus analytical investigations •Descriptive investigations Based upon cases only Look at time, place and person epidemiology Raise hypotheses • Analytical investigations Based upon a study of the cases and non-cases Compare: • Cases with controls with respect to exposure • Exposed with unexposed with respect to incidence Test hypotheses • How could we test the hypothesis for the Baripada investigation? Investigations
- 22. 22 Steps of afull outbreak investigation using analytical epidemiology to identify the source of infection 1. Determine the existence of an outbreak 2. Confirm the diagnosis 3. Define a case 4. Search for cases 5. Generate hypotheses using descriptive findings 6. Test hypotheses based upon an analytical study 7. Draw conclusions 8. Compare the hypothesis with established facts 9. Communicate findings 10. Execute prevention measures Requires assistance from qualified field epidemiologist (FETP)
- 23. 23 Acute hepatitis Control Total Drunk waterfrom river bed pump 493 134 627 Did not drink pump water 45 404 449 Total 538 538 1076 92% of cases (493/538) drunk water from suspected source versus 25% (134/538) of controls Consumption of pipeline water among acute hepatitis (E) cases and controls, Baripada, Orissa, India, 2004 Analytical epidemiology compares cases and non cases or exposed versus unexposed to test the hypothesis generated on the basis of the time, place and person description Investigations
- 24. 24 3. Monitoring thesituation • Trends in cases and deaths • Implementation of containment measures • Stocks of vaccines and drugs • Logistics Communication Vehicles • Community involvement • Media response Investigations
- 25. 25 4. Declaring theoutbreak over • Role of the district surveillance officer / Medical health officer • Criteria No new case during two incubation periods since onset of last case • Implies careful case search to make sure no case are missed Investigations
- 26. 26 5. Review ofthe final report • Sent by medical officer of the primary health centre to the district surveillance officer / medical and health officer within 10 days of the outbreak being declared over • Review by the technical committee Identification of system failures Longer term recommendations Investigations
- 27. 27 Outbreak preparedness: A summaryof preparatory action • Formation of rapid response team • Training of the rapid response team • Regular review of the data • Identification of ‘outbreak seasons’ • Identification of ‘outbreak regions’ • Provision of necessary drugs and materials • Identification and strengthening appropriate laboratories • Designation of vehicles for outbreak investigation • Establishment of communication channels in working conditions (e.g., Telephone) Management
- 28. 28 Managerial aspects ofoutbreak response • Logistics Human resources Medicines Equipment and supplies Vehicle and mobility Communication channels • Information, education and communication • Media Daily update Management
- 29. 29 Control measures foran outbreak • General measures Till source and route of transmission identified • Specific measures, based upon the results of the investigation Agent • Removing the source Environment • Interrupting transmission Host • Protection (e.g., immunization) • Case management Management
- 30. 30 Take home messages 1.Do not ignore or hide outbreaks 2. Respond to early warning signals 3. Investigate outbreaks to: Control the current outbreak Learn about the disease in the local setting 4. Outbreaks require an organized, well managed response
- 31. 31 Additional reading • CDCtext book on principles of epidemiology • Section 5 of operations manual • Module 8 of training manual Detection
Editor's Notes
- #2 The usual warming up questions for a few minutes.
- #3 The outline of the session.
- #4 The difference between endemic and epidemic. Self explanatory.
- #5 The difference between outbreak and epidemic. The take home message is: There is no formal difference. You are the one who decide how much importance you want to give to the event. If you are having lots of measles and none wants to help, call it a major epidemic. If it is a cluster well under controlled that the press is blowing out of proportion, call it a small outbreak.
- #6 This slide is a booster dose for the lecture on alert.
- #7 The early warning signals for an outbreak. Provide additional examples.
- #8 The First Information Report is a quick document, a sort of post card from the field that says: This is the alert, we are on our way, we will investigate and we will bring more information.
- #9 Self explanatory.
- #10 An outbreak comes from a break in the balance between the host, the environment and the agent. We need to understand this breach of balance to propose effective control measures. Hence the objectives of the investigations.
- #11 This is an important slide. There is a balance between investigation and control measures in outbreak response. Underline the 2 x 2 table matrix that is the way we think in epidemiology ;-)
- #12 The steps in outbreak response. Response is a broader term that covers (1) investigations and (2) control measures.
- #13 The step 1 of the outbreak investigation. We need to verify not to fall in the trap of pseudo outbreaks.
- #14 Step 2. The rapid response team is the strong arm of outbreak response. Multi-disciplinary is the key word. The slide also introduces the key notion of the two levels: Generating hypotheses on the basis of descriptive information Testing hypotheses on the basis of analytical methods. We want people to be proficient at the first and aware of the second.
- #15 A flow chart presentation of the same. If the descriptive epidemiology suggests you are dealing with a very well known classical scenario, you may not need analytical methods. But if there is something you do not understand, then you do need them.
- #16 The following few slides will go through an example of hypothesis generation and testing. It is an hepatitis E outbreak in Orissa.
- #17 This is the TIME information: What does it suggest? Give a moment to the participants. Encourage them to follow the (1) describe and (2) analyze/ interpret steps. Probably a point source outbreak. It leads us to look into what happened one month earlier: There was a strike in the municipal water treatment plant.
- #18 This is the PLACE information. Give a moment to the participants. Encourage them to follow the (1) describe and (2) analyze/ interpret steps. It seems the disease clusters around the one source of water supply that comes directly from the river.
- #19 This is the PERSON information. Give a moment to the participants. Encourage them to follow the (1) describe and (2) analyze/ interpret steps. The attack rate by age and sex is highly compatible with HEV.
- #20 Here we summarize the time, place and person information to “connect the dots” and come with a picture that generates an hypothesis: The hypothesis reads as: The river water may have been supplied untreated in the area of the outbreak because of the strike at the water treatment plant
- #21 Again we emphasize the difference between the two levels: Descriptive / hypothesis raising Analytical / hypothesis testing We want them to be proficient at the first and aware of the second. Brainstorm with the participants how to go about the analytical approach.
- #22 If we go for a fully fledged investigation with analytical methods, we will use the classical 10 steps. But that is beyond the skills we expect from the participants of the course. We would need help from a 2-year scholars of a Field Epidemiology Training Programme.
- #23 If we get back to the Baripada HEV example, this is how the analytical epidemiology was approached with a case control study. See the language in purple at the bottom: The objective is to remain at a broad, conceptual level.
- #24 Back to our steps in the investigations. Now step 3: Monitoring the situation.
- #25 And step 4.
- #26 … and step 5.
- #27 But we do not wait for an outbreak to happen. We want to be prepared. Here is a list of the actions to undertake to be ready.
- #28 So far we have gone through the logical, methodological , intellectual aspects of outbreak investigations. But there is a managerial aspect also.
- #29 The control measures to undertake. They should be based on the results of the investigations. If the outbreak says it was the food handler of the village there is no point in chlorinating the well!
- #30 The take home messages.
- #31 Here are the additional resources you can use.