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Investigation of an Epidemic

Epidemic investigation

drprabhakar
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Investigation of an Epidemic

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  1. INVESTIGATION OF AN EPIDEMIC Dr Manish Prabhakar Moderator- Dr Abhay Ambilkar

  2. FRAMEWORK Introduction Definitions Objective of epidemic investigation Reasons to investigate How to recognize outbreak/epidemic Goals of investigations Example of an epidemic Steps in investigation of epidemic

  3. Introduction It is an emergency situation and provides opportunities to use epidemiological knowledge for immediate control of disease. Cholera, food poisoning, influenza, malaria, chikungunya fever, Hepatitis A and anthrax as causes of epidemics Epidemiological Investigation usually conducted in outbreak situation The main reason for conduction epidemiological Investigation are -To determine cause of outbreak -To Implement control measures to prevent additional illness

  4. . • Outbreak- An increase in the incidence of a disease above what is normally expected in localized area over a specific period of time • limited to a small focal area • Pseudo outbreak: Increase in detection of true cases that does not represent an outbreak • Epidemic- - Occurrence in a community or a area of cases of a disease that are clearly in excess of what is expected - Covers large geographic areas • Endemic- • The habitual presence of a disease within a given geographic area • Pandemic- • A worldwide epidemic Cluster : Refers to a group of cases in a specific time and place

  5. Objectives of an epidemic investigation To determine magnitude of the epidemic and it’s distribution in terms of time, place and person To identify risk factors , to identify the cause, sources of infection, carrier and modes of transmission measures necessary to control the epidemic recommendations to prevent recurrence

  6. Reason of investigation Identify the Source (eliminate it) Develop strategies to prevent future outbreak May represent breakdowns in public health measures. Evaluate existing prevention strategies, e.g., vaccines Describe new diseases and learn more about disease learn epidemiology of infectious diseases Address public concern about the outbreak

  7. How to recognise Epidemic Recently WHO recommends global alert and response system (GAR). Early warning which is timely surveillance systems that collect information on epidemic prone diseases in order to trigger prompt public health interventions. Relies on an in-depth review done by epidemiologists of the data coming in Surveillance system Reporting : Healthcare settings, laboratories, pharmacies Surveillance is the collection, analysis, interpretation and dissemination of information about a selected health event. This information is important to plan, implement and evaluate a health program.

  8. Goal of Epidemics Identify the etiologic agents Identify the reservoir(s) Identify the mode of transmission Apply control and prevention measures Eliminate the reservoir(s) and transmission Prevent future outbreaks

  9. Epidemic investigation of an unknown fever at two villages of Murshidabad district, West Bengal Unknown fever epidemic – May- June, 2003 Nearby health facility- Rural Hospital Total number of affected villages - 4 (Kuchidanga, Kadamtala, Janardanpur and Natundiar) Population of affected villages - 10432 Date of first attack - 26.5.2003 Date of first information - 2.6.2003 at 6.00 PM Total number of fever cases - 258 Total number of death – 19 Compare- corresponding months of previous 3 years

  10. Example cont...

  11. 10 clotted blood, 7 whole blood, 7 slides, and 7 in Minimum. Essential Media

  12. Steps in investigation of epidemic Confirmation of the existence of an epidemic Verification of diagnosis Develop valid case definition Develop line listing & Rapid search of cases Develop epidemiological case sheet Data analysis Formulation of hypothesis Testing hypothesis Refine hypothesis Control measures Writing a report Monitoring the situation Declaring the outbreak to be over Review of final report

  13. I. Confirm the existence of an epidemic • The first step in investigating an epidemic is to detect it • Ways of detection- • review the data from the routine surveillance • Hospital data • Health workers in PHC • Private practitioners • Rumour registers • Media • MO nearest to the location should confirm

  14. . • MO should check • Clustering of cases or deaths in time and/or space • Unusual increase in cases or deaths • if many deaths have occurred • Compare current number of cases with past experience (three years in same population) • Even a single case of measles, AFP, Cholera, Plague, dengue or JE • Acute febrile illness of unknown aetiology • Etiology, the source and the route of transmission is known-specific control measures , If any one of them is unknown- investigate outbreak • Sending Rapid response team -Team of Epidemiologist, clinician, microbiologist

  15. 2. Verification of diagnosis • Medical investigation- • clinical diagnosis • History identify the possible source, routes of transmission and contacts • Laboratory investigation- • Samples • mode of collection • method of transportation • laboratory • Epidemiological investigation- • basic aim- identify the possible source, routes of transmission • may ask for tests

  16. 3. Develop valid case definition • Searching of cases, involve a number of medical officers/ paramedical staff. • Adequately sensitive as well as adequately specific • to ensure uniformity during the investigations • Cases in 3 categories- • Suspect-for paramedical staff • Probable- for GP • Definite- for MO • During hypothesis formulation- more sensitive definition • Hypothesis tested or refined- definition made more specific removing the “suspect” category

  17. 4. rapid search of cases & Develop Line -listing • Rapid search- • house to house survey • Hospital data • Asking patient about other cases • Till twice the incubation period of disease since last case occurrence • a serial chronological listing of all the known cases • Benefits- possible sources, population at risk, place and time distribution

  18. 5. Develop the epidemiological case sheet Personal and clinical details of all cases & person exposed but unaffected Information collected should be relevant to disease under study If large outbreak- data collected from random sample

  19. 6. Data analysis • Ongoing process • Time, Place, person distribution

  20. 7. Formulation of hypothesis • Review all the investigative findings • Formulate hypothesis • Possible source • Causative agent • Possible mode of spread • People at risk • Environmental factors • Guide further investigation

  21. 8.Testing hypothesis • Compare attack rate in various groups for those exposed and those not exposed to each suspected factor.

  22. 9. CONTROL OF EPIDEMIC

  23. 10. Writing a report Preliminary report by nodal MO Daily situation updates Interim report by RRT Final report

  24. 11. Monitoring the situation • on a regular basis • Point to be monitored • The trends in the cases and deaths. • The containment measures that are being implemented • Drugs / vaccine stock • Logistic issues – communications, vehicles, • Community involvement • Media response • till the outbreak is officially declared to be over

  25. 12. Declaring the outbreak to be over no new cases for a period of 2 incubation periods since the onset of the last case Active search No case should be missed

  26. 13. Review of the final report within 10 days of the outbreak being declared to be over Based on this report Recommendations for improvement to prevent recurrence of epidemic

  27. Flowchartin investigation of epidemic Unusual health event Yes No Is this an outbreak Etiology, source and transmission known? Institute control measures Yes No Develop Hypothesis regarding source, transmission, etiology and people at risk Describe outbreak in terms of Place, time and Person Further Investigation (Clinical, Laboratory, Epidemiological) Institute control measures Does the Hypothesis fit with the Facts? Yes Special studies No

  28. Epidemic preparedness Formation & training rapid response team Regular review of the data Identifying outbreak seasons Identifying outbreak regions necessary drugs and materials including transport media Identifying and strengthening the appropriate labs Designating vehicles, ensuring it’s working condition communication channels in working condition.

  29. References Vaughan JP, Morrow RH. Manual of epidemiology for district health management. Geneva: World health organization; 1989 Outbreak investigation, reponse & control. IDSP module. Bhalwar R. Textbook of public health and community medicine.1st ed. Pune; 2009 Epidemic Investigation. National Institute of Cholera And Enteric Diseases (NICED) Annual Report 2003-2004

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