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INVESTIGATION OF AN EPIDEMIC
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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 usefulto 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 forthat 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 havea detailed and current map of the area. It shouldcontain information concerning natural landmarks, roadsand location of all dwelling units in each road or inisolated areas. Area may be divided into segments,using natural landmarks as boundaries. This may againdivided into smaller sections. Within each section thedwelling units may be designated by numbers.
B.Counting of the population
A complete census of the population by age and sex byhouse to house visits(if the general population affected)
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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 ofdisease,Signs&Symptoms of illness,Personnel contact athome,work,school and other places,Special events suchas parties attended, Foods eaten, and exposure to
common vehicles such as water, food and milk, visits outof the community, History of injections, or bloodproducts, attendance at large gatherings. If the outbreak 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 inthe home,family,neigbourhood,school,workplace,
having an onset within the incubation period ofthe index case, cases admitted to local hospitalsshould also be taken into consideration. Searchshould be carried out every day till the area is
declared free of epidemic. This period is usuallytaken as twice the incubation period of the diseasesince the occurrence of last case
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DATA ANALYSIS
A . Prepare a
chronologicaldistribution ofdates of onsetand construct
an epidemiccurve
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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 investigation4. 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 elsewhereOccurrence 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 teamsa. 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 occurrence2. 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 entry3. 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 causes3. 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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HEALTH INSPECTOR
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