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

A. 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

A . Prepare a chronological distribution of dates of onset and construct an epidemic

curve

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

The report should be complete

and convincing.

WRITING THE REPORTS

CONTENTS OF REPORT

1. Back ground

2. Historical data

3. Methodology of investigation

4. Analysis of data (clinical data,Epideiological

data, modes of transmission, Lab data,

Interpretation of data)

5. Control measures

6. Evaluation

7. 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

a. House to house

b. Retrospective

c. Prospective

Collection of Lab. Specimens

Lab techniques

ANALYSIS OF DATA

A. 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

1. Source of infection

2. Route of excretion and portal of entry

3. Factors influencing transmission

D. Lab data

1. Isolation of agents

2. Serological confirmation

3. Significance of results

ANALYSIS OF DATA

E. Interpretation of data

1. Comprehensive picture of the outbreak

2. Hypotheses on causes

3. 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