Investigation of epidemic

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Investigation of epidemic:

Investigation of epidemic Dr. Nitin Solanki Assistant Professor Dept of Community Medicine Gujarat Adani Institute Of Medical Science

To explain the various epidemiological concepts & terms To describe the general steps of epidemic investigation :

To explain the various epidemiological concepts & terms To describe the general steps of epidemic investigation 2 Learning objectives

Some definitions:

Some definitions Epidemics: The “ unusual” occurrence in a community or religion of disease, specific health related events or health related behavior clearly in excess of expected occurrence. Outbreak: Small , usually localized epidemic in the interest of minimizing public alarm. So no help need form outside the region. Endemic: Constant present of disease or infectious agent within given geographical area or population group, Without importance from outside.

Objective of Epidemic Investigation:

Objective of Epidemic Investigation To define magnitude of epidemic or involvement in terms of Time, Place and Person. To determined particular conditions and factor responsible for Epidemic To indentify cause, source and models of transmission for control measure. To make recommendation to prevent recurrence

Early warning signals for an outbreak:

5 Early warning signals for 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

Outbreak Detection and Response:

DAY CASES Lab Confirmation Outbreak Detection and Response Response Opportunity for control Detection/ Reporting First Case Credit to control d/s

Outbreak Detection and Response:

DAY CASES Outbreak Detection and Response First Case Detection/ Reporting Confirmation Investigation Opportunity for control Response

Ten Step for epidemic investigation:

Ten Step for epidemic investigation Verification of diagnosis. Conformation of existence of epidemic. Define population at Risk. Rapid search for all cases and their characteristics. Data analysis according to time, place and person. Formulation of hypothesis. Testing of hypothesis. Evaluation of Ecological factors. Further investigation of population at Risk Writing the report and Execute control and prevention measures 8

Slide 9:

Verification of diagnosis. Is the first step to start epidemic investigation as it may happen sometime that report may be spurious, and may be due to misinterpretation of signs and symptoms by the lay public. Clinical diagnosis can be obtained through standard laboratory techniques such as serology and/or isolation of agents. But one should not wait for Lab result to come for initiating investigation. Ten Step for epidemic investigation

Ten Step for epidemic investigation:

Ten Step for epidemic investigation Verification of diagnosis. Conformation of existence of epidemic. Done by comparing the disease frequency with same period of previous years. An arbitrary limit of 2SE of epidemic occurrence is used to define the epidemic threshold for Common diseases. NO such comparison is required for common source epidemic. Single case as epidemic in Polio, Measles, Plague, JE, Cholera. 10

Ten Step for epidemic investigation:

Ten Step for epidemic investigation Verification of diagnosis. Conformation of existence of epidemic. Define population at Risk. Obtaining map of that area: Called as Spot MAP. Counting the population: for the counting the denominator . It might be entire population or subgroup of the population. - for that use census data or house to house survey. - calculate Attack Rate 11

Slide 12:

12 Attack rate Attack rate = No. of persons exposed to an infectious agent and fell ill Total no. of persons exposed to the infectious agent Need for denominator (all exposed)

Ten Step for epidemic investigation:

Ten Step for epidemic investigation Verification of diagnosis. Conformation of existence of epidemic. Define population at Risk. Rapid search for all cases and their characteristics. - Medical Survey: - Epidemiological Case sheet: - Searching for more case: 13

Ten Step for epidemic investigation:

Ten Step for epidemic investigation 3. Define population at Risk. 4. Rapid search for all cases and their characteristics. 5. Data analysis according to time, place and person. - Time : Construct Epidemic Curve - Place: Construct Spot Map -Person: Analysis of data with age, sex, occupation and other possible risk factor. Main purpose of data analysis is to identify common event or experience, and group involvement in that experience. 14

Example: Outbreak of acute hepatitis (E) in AMC , 2009:

15 Example: Outbreak of acute hepatitis (E) in AMC , 2009 Identification of a cluster of acute hepatitis cases Diagnosis: HEV infection Use time, place and person analysis of surveillance data to suggests hypotheses

Cases of acute hepatitis (E) by date of onset, AMC , January-March 2009:

16 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 treatment stopped Cases of acute hepatitis (E) by date of onset, AMC , January-March 2009 Time: A cluster a month after a strike in the water treatment centre Investigations

Attack rate of acute hepatitis (E) by residence, AMC , India, 2009:

17 Sabarmati basin river Attack rate of acute hepatitis (E) by residence, AMC , India, 2009 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

Attack rate of acute hepatitis (E) by age and sex, AMC , India, 2009:

18 Attack rate of acute hepatitis (E) by age and sex, AMC , India, 2009 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 Person: Attack rate compatible with HEV Investigations

What hypotheses would you generate for the outbreak of acute hepatitis (E) in AMC , 2009?:

19 What hypotheses would you generate for the outbreak of acute hepatitis (E) in AMC , 2009? 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

Ten Step for epidemic investigation:

Ten Step for epidemic investigation 5. Data analysis according to time, place and person. Formulation of hypothesis. - to explain (a) possible source (b) causative agent (c) possible mode of spread and (d) the environmental factor which enabled it to occur. 7. Testing of hypothesis. - All hypothesis weighted by comparing with the attack rate in various group for those who exposed and those who not exposed.

Ten Step for epidemic investigation:

Ten Step for epidemic investigation 6. Formulation of hypothesis. 7. Testing of hypothesis. Evaluation of Ecological factors. - Like Sanitation status of eating establishment. - Water and Milk Supply - Breakdown of water supply system - Movement of human Population - Atmospheric Change like Temperature, Humidity, Pollution, - Population dynamics of insects and animal reservoirs. 21

Ten Step for epidemic investigation:

Ten Step for epidemic investigation 7. Testing of hypothesis. 8. Evaluation of Ecological factors. 9. Further investigation of population at Risk - To obtaining additional information with help of - Medical examination, - Screening Test, - Examination of suspected food, - Blood and faeces sample, - biochemical testing. This will help in classification of all member as to 1. Exposure or not 2. Ill or Not.

Ten Step for epidemic investigation:

Ten Step for epidemic investigation 9. Further investigation of population at Risk 10. Writing the report and Execute control and prevention measures - Report should be complete and convincing - Implementation of temporary control measures on the basis of know facts about disease. - Control measure may be modify when new knowledge was acquired by investigation.

Suggested Reading:

Suggested Reading Park Textbook of Preventive and Social Medicine :K Park 20 th ed.M /s Bhanot Jabalpur India.2009 Epidemiology – Leon Gordis 4 th Edtion (Oxford University Press)

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