Investigation of an epidemic

OBJECTIVES To define the magnitude of the epidemic outbreak or Involvement in terms of time, place and person To determine the particular conditions and factors responsible for the occurrence of the epidemic To identify the cause, source of infection, and modes of transmission to determine measures necessary to control the epidemic and To make recommendations to prevent recurrence

VERIFICATIONS OF DIAGNOSIS It is the first step ,do as quickly as possible. It is not necessary to examine all the cases to arrive at a diagnosis. clinical examination of a sample of cases may well suffice. Lab investigations are most useful to confirm the diagnosis but the epidemiological investigations should not be delayed until the lab results are available

CONFIRMATION OF THE EXISTENCE OF AN EPIDEMIC Second step. Done by comparing the disease frequencies during the same period of previous years. An epidemic is said to be exist when the no. of cases is in excess of the expected frequency for that population based on past experience

DEFINING THE POPULATION AT RISK A.Obtainig a map of the area. Before beginning the investigation it is necessary to have a detailed and current map of the area. It should contain information concerning natural landmarks, roads and location of all dwelling units in each road or in isolated areas. Area may be divided into segments, using natural landmarks as boundaries. This may again divided into smaller sections. Within each section the dwelling units may be designated by numbers. B.Counting of the population A complete census of the population by age and sex by house to house visits(if the general population affected)

RAPID SEARCH FOR ALL CASES AND THEIR CHARECTERISTICS Medical survey To identify all cases including those who have not sought medical care and those possibly exposed to risk. Complete survey will pick-up all affected individuals with symptoms or signs of disorder.

RAPID SEARCH FOR ALL CASES AND THEIR CHARECTERISTICS B.Epidemiological case sheet This includes: Name,Age,Sex,Occupation,Socialclass,Travell, History of previous expossure,Time of onset of disease,Signs&Symptoms of illness,Personnel contact at home,work,school and other places,Special events such as parties attended, Foods eaten, and exposure to common vehicles such as water, food and milk, visits out of the community, History of injections, or blood products, attendance at large gatherings. If the out break is large-random sample.

RAPID SEARCH FOR ALL CASES AND THEIR CHARECTERISTICS C.Searching for more cases: Patient may be asked if he knew of other cases in the home,family,neigbourhood,school,workplace, having an onset within the incubation period of the index case, cases admitted to local hospitals should also be taken into consideration. Search should be carried out every day till the area is declared free of epidemic. This period is usually taken as twice the incubation period of the disease since the occurrence of last case

DATA ANALYSIS B. Place prepare a spot map of cases(geographic distribution) and if possible their relation to possible sources of infection eg:water supply, air pollution, foods eaten, occupation etc.Clustering of cases may indicate a common source of infection

DATA ANALYSIS C.Person Analyze the data by age,sex,occupation and other possible risk factors. Determine the attack rate/ case fatality rate

FORMULATION HYPOTHESES On the basis of time-place-person/agent-host-environment model, formulate hypotheses to explain the epidemic in terms of A. Possible source B. Causative agent C. Possible mode of spread and D. The environmental factors which enabled it to occur

TESTING OF HYPOTHESES All possible hypotheses need to be considered and weighed by comparing the attack rates in various groups for those exposed, those not exposed to each suspected factor

EVALUATION OF ECOLOGICAL FACTORS Evaluation of the circumstances involved should be carried out to undertake appropriate measures to prevent further transmission Sanitary status of eating establishments, water and milk supply, breakdown in the water supply system, movements of the human population, atmospheric changes such as temp.,humidity and air pollution, population dynamics of insects, and animal reservoir Source-reservoir-modes of transmission

FURTHER INVESTIGATION OF POPULATION AT RISK Medical examination, Screening tests, examination of suspected food,faeces or blood samples, biochemical studies,assesment of immunity status

WRITING THE REPORTS The report should be complete and convincing.

CONTENTS OF REPORT Back ground Historical data Methodology of investigation Analysis of data (clinical data,Epideiological data, modes of transmission, Lab data, Interpretation of data) Control measures Evaluation Preventive measures

BACK GROUND Geographical location Climatic conditions Demographic status(Population pyramid) Socio-economic situation Organization of health services Surveillance&early warning systems Normal disease prevalence

HISTORICAL DATA Previous occurrence of epidemics 1.Of the same disease 2.Locally or elsewhere Occurrence of related diseases if any In the given area In other area Discovery of first case of the present outbreak.

METHODOLOGY OF INVESTIGATION Case definition, Questionnaire used in epidemiological investigation Survey teams House to house Retrospective Prospective Collection of Lab. Specimens Lab techniques

ANALYSIS OF DATA Clinical data 1.Frequency of signs&symptoms 2. Course of disease 3. Different diagnosis 4. Death or sequelae rates B.Epidemiological data 1.Mode of occurrence 2. In time 3.By place 4. By population groups

ANALYSIS OF DATA C. Modes of transmission Source of infection Route of excretion and portal of entry Factors influencing transmission Lab data Isolation of agents Serological confirmation Significance of results

ANALYSIS OF DATA E. Interpretation of data Comprehensive picture of the outbreak Hypotheses on causes Formation and testing hypotheses by statistical analysis

CONTROL MEASURES Definitions of strategies and methodology of implementation Constraints Results

EVALUATION Significance of results Cost/Effectiveness Preventive measures

THANK YOU SUGUNAN.KR HEALTH INSPECTOR PHC PINDIMANA&PUNNEKKAD MOB:9446024671

Investigation of an epidemic

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