investigation of an epidemic
TRANSCRIPT
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INVESTIGATION OF AN
EPIDEMIC
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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
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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
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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
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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)
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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.
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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.
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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
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DATA ANALYSIS
A . Prepare a chronological distribution of dates of onset and construct an epidemic
curve
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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
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DATA ANALYSIS
C.Person
Analyze the data by age,sex,occupation and
other possible risk factors. Determine the
attack rate/ case fatality rate
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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
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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
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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
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FURTHER INVESTIGATION OF
POPULATION AT RISK
Medical examination, Screening tests,
examination of suspected food,faeces or blood
samples, biochemical studies,assesment of
immunity status
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The report should be complete
and convincing.
WRITING THE REPORTS
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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
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BACK GROUND
Geographical location
Climatic conditions
Demographic status(Population pyramid)
Socio-economic situation
Organization of health services
Surveillance&early warning systems
Normal disease prevalence
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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.
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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
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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
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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
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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
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CONTROL MEASURES
Definitions of strategies and methodology of
implementation
Constraints
Results
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EVALUATION
Significance of results
Cost/Effectiveness
Preventive measures
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