survillance.pptx

What is epidemiologic
surveillance?
It is the systematic collection, analysis,
interpretation and dissemination of health
related data in an ongoing basis.
 Surveillance provides ‘information for
action’ which can be used to investigate,
prevent and control disease in a community.
 Surveillance can be conducted globally,
regionally, nationally or locally.
2

Epidemiological Surveillance
• Definition:--Surveillance is the continues
search of the factors that determine the
occurrence and distribution of the disease
and other related events through systemic
collection of data.
3

Purpose of surveillance:
The main purpose of surveillance includes:-
• prediction and early detection of the
outbreak. To be able to identify diseases,
injuries, hazards and other health related
factors as early as possible, i.e.
• provide scientific baseline data and
information for priority setting, planning,
implementing and evaluating disease control
program
• Define the magnitude and distribution of
disease by time. place and person dimension
4

Source of data for surveillance
• Morbidity and mortality reports
• Special reports of field investigation of
epidemic and of individual cases.
• Isolation and identification of infections
agents by laboratories
5

Types of surveillance
1. Passive surveillance
2. Active surveillance
3. Sentinel Surveillance
.
6

1. Passive surveillance
• Passive surveillance may be defined as a
mechanism for routine surveillance based
on passive case detection and on the
routine recording & reporting system.
7

Passive surveillance cont…
• It involves collection of data as part of
routine provision of health services
• Passive surveillance is that in which health
care providers send reports based on a
known set of rules and regulations
8

Advantages
–It covers a wide range of problems.
–Does not require special arrangement
–Relatively cheep
9

Disadvantages
• The information generated is to a large extent
Unreliable, incomplete, & in accurate
• Data is not available on time
• May not be found the kind of information
desired
• It lacks representatives as it is from health
institution
• No feed back system.
10

Cont…
2. Active Surveillance
 Is defined as method of a data collection
usually on specific disease for relatively
limited period of time.
A condition in which the health providers
collect reports of a disease by moving to the
community with a morbidity of interest.
• It involves collection of data from communities.
E.g. house to house survey
11

Conditions in which active surveillance is appropriate
Active surveillance has limited scope. Unlike Passive
surveillance, it cannot be used for routine purposes.
There are certain conditions where active
surveillance is appropriate. these conditions are:
• For periodic evaluation of an ongoing program
• For programs with limited time of operation such a
eradication program
• In unusual situations such as:-
- New disease discovery.
- New mode of transmission,
- When a disease is found to affect a new subgroup
of the population.
- When a previously eradicated disease reappears
12

Techniques employed to collect information for
active surveillance are
• Sending out letter describing the situation and
asking for report or
• Making a telephone call or
• visit the facilities to collect information on
cases
• Alerting the people directly, usually through
local media to come to health facility under
questions.
• Asking patients of the particular disease if
they know any one else with the same condition
13

• Advantage of active surveillance
• the data collected is complete and
accurate
• Information collected is timely
• Disadvantages
• Requires good organization
• It is expensive
• Requires skilled man power
• It is not continues process
• Directs to specific disease conditions
14

Cont…
3. Sentinel Surveillance
• Using a pre-arranged sample of reporting
sources to represent all conditions in the
a specified community.
15

Surveillance has been going on the different
parts of the world:-
Examples
• global surveillance – poliomyelitis, influenza,
RF. Epidemic typhus
• WHO special program on tropical disease-
malaria, leprosy, Filariasis
• WHO-EPI diseases- vaccine preventable
disease
16

Selection criteria of disease for surveillance
The importance of a health event to be included
in surveillance system, it should be assessed
by:
1. The current impact of the health event
• Having high Incidence/ prevalence
• Mortality (overall and age specific rates)
• Morbidity (Hospitalization, disability) (top
morbidity )
• Severity (case fatality rate)
• Health care costs
eg Malaria, Pneumonia, Diarrheal ,dis.TB,
HIV/AIDS
17

Cont…
2. Having epidemic potential (eg. Measles, cholera,
meningitis)
3. Surveillance required internationally (eg Plague,
yellow fever, cholera)
4. Having available and effective control and
prevention interventions (eg Schistosomiasis,
Onchoserciasis, trypanosomiasis)
5. Can easily be identified using simple case
definitions
6. Having intervention program already found in
the country, (eg EPI, IMCI)
18

Once diseases for surveillance are selected we
should do the following items:
1. Case definition of diseases included in the
surveillance. (Confirmed, probable and
possible diagnosis)
2. Determine the population under surveillance
3. Time period of data collection(immediate,
weekly, and monthly)
4. Source of data, who would report etc.
5. How data are handled (confidentiality)
19

Cont…
Case definition of diseases included in the
surveillance.
Case definition
• A case definition is a set of criteria used
to decide a person has a particular disease.
• If the same case definition is agreed to be
used by every body within a country or
across a boundary it is called standardized
case definition
20

Case definition
- It includes Criteria: Signs and symptoms with or without
a laboratory test
-Restriction by time, place and person can be done
depending on the nature of the disease
Classification of case definition
1.Confirmed: a case definition by appropriate lab. Test
2. Probable: a case with typical clinical features of the
disease without laboratory confirmation
3. Possible/ Suspect: a case with few of the typical clinical
features.
21

Example of case definition for malaria
Confirmed
Malaria
Probable
Malaria
Possible/
Suspect malaria
Confirmed by
laboratory
test
Presence of
chills, fever,
headache,
arthralgia, back
pain … etc, of
sudden onset
without
laboratory
confirmation
Presence of
fever and
headache of
sudden onset
without
laboratory
confirmation
22

Time period of data collection
• It is useful to identify problems and solve
timely
There are three periods of reporting
1. Immediate reporting:
A. For diseases that include presence of a
suspect consider eg. Polio, Cholera, plague,
viral hemorrhagic fever, Yellow fever
B. a suspected epidemic when threshold is
crossed On weekly basis: for epidemic prone
diseases. eg Malaria, meningitis
3. On monthly basis: for Routine surveillance
Tuberculosis, Leprosy, AIDS cases
23

Features of a good surveillance system
• Using a combination of both active and
passive surveillance techniques
• Timely notification
• Timely and comprehensive action taken
in response to notification
24

Activities in surveillance
Steps to be followed in surveillance system
Different activities carried out under surveillance
are:
• Data collection and recording:- an essential item of
information is diagnosis
• Data compilation, analysis and interpret:-
registered cases by person, place, time
• Formulation of Recommendation:- based on analysis
& interpretation made
• Dissemination and feed back:- result should pass
through relevance persons and institutions
concerned 25

Epidemic Investigation &
Management
26

Learning Objectives
At the end of this unit the student is
expected to:
• Define epidemic
• Identify types of epidemic
• Describe the different steps in the
investigation of epidemic
• Discuss the management of epidemic
27

EPIDEMIC
An epidemic –
• It is defined as the occurrence of any health-
related condition in a given population in excess
of the usual frequency in that population.
• There are three important points to consider in
this definition.
28

Cont…
1. An epidemic can occur not only to acute
infectious diseases, but also to chronic and
non-infectious diseases.
2. There is no minimum number of cases of
disease required to constitute an epidemic.
3. One should know the usual frequency of the
disease in that population by surveillance to
detect an epidemic of disease.
29

PATTERNS OF EPIDEMICS
Two principal types are well recognized. These
are –
-the common source and
-propagated/progressive.
The two types can be distinguished by plotting
an epidemic curve.
An epidemic which shows the features of both
types is referred as mixed.
30

Epidemic curve
• It is a histogram describing number of cases
against time of onset.
• It uses time intervals on x-axis and cases on y-
axis
• It usually starts with a lead time on the x-axis
several incubation periods before the peak and
end it after the epidemic.
31

Common source epidemics
• Common source epidemics are caused by
exposure of a group of people to a common
infectious agent or a toxin. If the
exposure is brief and simultaneous all
exposed will develop the disease within one
incubation period - referred as point, or
point source epidemic/outbreak
32

Two principal types of epidemic
1. Point source (common source) epidemic: occur
as a result of the exposure of a group of
population to a common source (etiological
agent).
• Example, a contaminated water supply, or the
food in a certain restaurant.
• It can result from a single exposure of the
population group to the agent.
33

Cont…
A rapid rise and fall of an epidemic curve
suggests a point source epidemic- this is
called log-normal distribution.
34

The Point Source
Cases from a single brief exposure
0
10
20
30
40
50
60
Time
Cases
Source
Rapid rise Rapid Fall
Skew
Mean
Incubation
Maximum incubation
Minimum Incubation
35

Cont…
If the source of an outbreak remains for a
longer time, days, weeks or longer either
continuously or intermittently
or there will be multiple exposures with
variable incubation period, this will make an
epidemic curve with no clear peak and the
duration of the outbreak will be prolonged.
36

Cont…
Continuous common source
-makes wide peak in the epidemic curve,
because of the range of exposures and range
of incubation periods.
Intermittent common source - results in an
irregular pattern of the epidemic curve
that reflects the intermittent nature of the
exposure.
37

A continuous common source
0
2
4
6
8
10
12
14
16
Time
Cases
Flat peak
38

2. Propagated or progressive epidemic:
• Occurs as a result of transmission of an
infectious agent with a multiple source.
• It could be a transmission from person to person.
or the transmission could pass through a vector
from infected to healthy person
• E.g. malaria, measles, yellow fever.
• The epidemic curve is usually characterized by
presence of several peaks, a prolonged duration
and usually a sharp fall.
39

A Propagated Epidemic
Person to person transmission
0
5
10
15
20
25
0 4 8 12 16 20 24 28 32
Time
Cases
Source
Periodicity
40

Epidemic Investigation & Management
Levels of Disease Occurrence
• Diseases occur in a community at different levels
at a particular point in time. Some diseases are
usually present at a predictable level. This is
called the expected level.
• But sometimes they occur in excess of what is
expected.
• The examples of expected level are endemic and.
When the disease occur as epidemic, outbreak,
and pandemic it is considered as excess of what
is expected.
41

Causes of Epidemic
• Any communicable disease in an individual
or in community results from a dynamic
interaction b/n the agent, host and the
environment.
42

More specifically an epidemic may result
from the following
• A recent increase in amount or virulence
of the agent
• The recent introduction of the agent in
to setting where has not been before
• An enhanced mode of transmission so
that more susceptible hosts are
exposed.
• Some changes in the susceptibility of
the host response to the agent
43

Investigation of an Epidemic
• The purpose of investigation is to determine the
specific cause of the outbreak at the earliest
time and to take appropriate measure directed
at controlling the epidemic and preventing
future occurrence.
44

Questions that should be answered in investigating
to epidemic are:
• What is the Etiological agent responsible
• What is/are the predominate mode of
transmission
• What is the specific source
• E.g. human carrier, breeding sits for vector etc.
• What specific practice or environmental
deficiency have contributed
• What is the chain of event that lead to outbreak
45

Basic Principles of Epidemic Investigation
• Conduct multiple activities simultaneously
run: a dynamic process
• Maintain communication with officials,
stakeholders & public
• Record all steps taken in the process of
investigation and keep properly all
information gathered
• Careful and critical review of the literature
46

• Steps in Epidemic Investigation
1. Prepare for fieldwork
2. Verify (confirm) the existence of an epidemic
3. Verify (confirm the diagnosis).
4. Identify and count cases
- Prepare “case definition” before starting
identification of cases
5. Describe the epidemic with respect to
person, place and time
6. Identify the causes of the epidemic
7. Management of epidemic and follow up
47

• Case definition is defined as a standard
set of criteria to differentiate
• between cases and non cases. Cases can be
one of the following:
• Confirmed / definite: A case with
laboratory verification.
• Probable: A case with typical clinical
features but without laboratory
confirmation.
• Possible: A case with fewer of typical
clinical features.
48

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