12.
Epidemiological surveillance
Definition of Surveillance
• Surveillance is an on-going systematic
collection, analysis, interpretation and
dissemination of health-related data essential
to the planning, implementation, and evaluation
of public health practice.
Definition…
• Surveillance is a system of close observation of
all aspects of the occurrence and distribution of
a given disease through systematic
Collection,
tabulation,
analysis, and
dissemination of all relevant data pertaining to
that disease.
―Information for Action‖
Purpose of Surveillance
Knowledge of the distribution of health events
Rapid detection of outbreak
Public health planning and evaluation
Stimulating research
Describing natural history of diseases
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Selection Criteria of Disease for Surveillance
Magnitude of the disease
Feasibility of control measures
Need for monitoring and evaluating the
performance of a control program
Resource availability
ELEMENTS OF SURVEILLANCE SYSTEM
1. Case definition
2. Population under surveillance
3. Cycle of surveillance
4. Confidentiality
5. Incentives
1. Case definition
• CASE DEFINITION A set of criteria (not necessarily
diagnostic criteria) that must be fulfilled in order to
identify a person as representing a case of a
particular disease
Classification of case definition
Confirmed: a case definition by appropriate lab.
Test
Probable: a case with typical clinical features of
the disease without laboratory confirmation
Possible/ Suspect: a case with few of the
typical clinical features.
• Use case definition consistently!!
Major advantages of case definition
1) Facilitate early detection and prompt management
of cases
2) Useful in areas where there is no laboratory
3) Facilitate observation of trends
4) Facilitate comparison more accurately from area
to area.
Case definition cont’d
• Eg, surveillance definitions for Hepatitis A
ranges:
1. from ―Yellow eyes” to
2. documentation of specific acute phase
antibodies to the hepatitis A virus combined
with clinical signs of jaundice or laboratory
evidence of liver dysfunction.
• The first definition is very simple and could be
used by field staff with minimal training
Case definition cont’d.
• The second definition is appropriate in a
developed country where diagnostic testing is
routinely done to distinguish hepatitis types of A,
B, and C.
• For diseases with long latency or a chronic
course decision must be made regarding which
phase to monitor:
asymptomatic,
early disease, l
ate disease, death.
2. Population under surveillance
Target population can be:
individuals at specific institutions
Residents of a community
Residents of a nation, etc
3. Cycle of surveillance
Surveillance systems can be described as information
loops
The elements of the loop are:
1) occurrence of a health event
2) its detection by a health care provider
3) notification of health agency at different levels
4) analysis and interpretation of aggregate data
5) dissemination of the results.
• The loop is complete when the information is applied
• Addressing all these elements of the loop is crucial
The surveillance loop
Health care surveillance center
System
Reporting
Data
EVENT
ACTION Analysis interpretation
Inform
ation
Feedback , recommendation
4. Confidentiality
Personal identifying information is necessary to:
Identify duplicate reports
Obtain follow-up information when necessary
Provide services to individuals
use surveillance as the basis for detailed
Investigations
Protecting the physical security and confidentiality
of surveillance records is both an ethical
responsibility and a requirement for maintaining the
trust of participants
Elements of surveillance system cont.
While personal identifying information may be
needed at the local level, it is generally not
necessary for that information to be forwarded to
more central agencies.
In such cases codes can be used
5. Incentives to participation
• Providing information back to those who
contribute to the System
• This feed back may be in the form of reports
and seminars
TYPES OF SURVEILLANCE
• Three major types
1. Passive Surveillance
2. Active Surveillance
3. Sentinel Surveillance
1.Passive surveillance
• Passive surveillance is that in which
health care providers send reports based
on a known set of rules and regulations.
• Majority of public health surveillance
systems are passive
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Advantage Passive surveillance
Covers wide range of problems
ƒDoes not require special arrangement
ƒIt is relatively cheap
Covers a wider area
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Disadvantage of passive surveillance
Unreliable, incomplete and inaccurate data
ƒNot available on time
ƒƒLack of representativeness of the whole
population since passive surveillance is
mainly based on health institution reports
Most of the time, you may not get the kind
of information you desire
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2. Active surveillance
• Active surveillance is that in which
public health officials contact
providers to solicit reports of events
or diseases.
Limited to specific diseases over a
limited period of time, i.e epidemic.
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Advantages of active surveillance
• Data is complete and accurate
• ƒInformation collected is timely.
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Disadvantages of active surveillance
• ƒRequires good organization,
• ƒExpensive
• ƒRequires skilled human power
• ƒShort period of time(not continuous process)
• ƒDirected towards specific disease conditions
– Not cover many problem
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Conditions in w/c active surveillance is
appropriate
• For periodic evaluation of an ongoing program
• ƒFor programs with limited time of operation such as
eradication program
• In unusual situations;
– New disease discovery
– ƒNew mode of transmission
– ƒWhen a disease is found to affect a new subgroup
– of the population.
– ƒWhen a previously eradicated disease reappears.
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3. Sentinel surveillance
• Sentinel surveillance uses a pre-arranged
sample of reporting sources to report all
cases of one or more conditions.
Usually the sample sources are selected to
be those most likely to see cases.
Particularly in developing countries, sentinel
surveillance provides a practical alternative to
population-based surveillance
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Surveillance Activities
1. Data collection and recording
2. Data compilation, analysis and
interpretation
3. Reporting and notification
4. Dissemination of information
Data collection and recording
• Critical Information in Surveillance
– Person: Age, sex
– Time: onset of disease, reporting period
– Place: woreda, region
– Risk factors
– Number of cases (magnitude)
– Treatment outcome: deaths, recovery
(seriousness)
– Mode of treatment: inpatient/outpatient
Analysis of Surveillance Data
Descriptive analysis:
Distribution by time, place and person
Frequency of events
Calculate rates- need proper denominator
Observe trends
Compare current data with expected value,
identify differences, and assess the relevance of
the difference
Draw graphs to show long term (secular) trends
Disseminate surveillance data
To all stakeholders;
Those who provide the reports (health providers)
The community – affected/potentially affected
Decision makers
Disseminate report locally, nationally or globally; as
deemed necessary
Disseminate report timely and regularly
Disseminate through appropriate media:
newsletter or bulletin (paper or electronic)
Attributes/qualities of surveillance
• Surveillance systems can be judged using a list of attributes
(CDC 1988).
• This list can be used to evaluate an existing system or to
conceptualize a proposed system. These attributes are:
Sensitivity
Timeliness
Representativeness
Predictive value
Accuracy and completeness
Simplicity
Flexibility
Acceptability
Attributes of surveillance
A. Sensitivity
• To what extent the system identify all of the
events in the target population?
B. Timeliness
• Refers to the entire cycle of information flow,
ranging from information collection to
dissemination
Attributes of surveillance…
C. Representativeness
To what extent do events detected through the
surveillance system represent persons with the
condition of interest in the target population?
A lack of representativeness may lead to
misallocation of health resources
Attributes of surveillance…
D. Predictive value
To what extent are reported cases really cases?
To what extent are measured changes in trends
truly reflective of events in the community
Attributes of surveillance…
E. Accuracy and completeness of descriptive
information
To what extent are the sections of forms completed?
Is the information sufficiently reliable?
F. Simplicity
Are forms easy to complete?
Are procedures difficult?
Is data collection kept to a necessary minimum?
Attributes of surveillance…
G. Flexibility
• Can the system change to address new questions?
• Can it adapt to evolving standards of diagnosis or
medical care?
H. Acceptability
• To what extent are the participants in a surveillance
system enthusiastic about the system?
• Does the effort they invest yield useful information?
Reporting (Surveillance) requirements
The disease to be reported in Ethiopia should lie
under one of the following three categories
I. Epidemic Prone diseases
II. Diseases targeted for elimination/eradication
III. Diseases of public health importance
I. Epidemic prone diseases
• Cholera
• Dysentery
• Measles
• Meningitis
• Plague
• Viral Hemorrhagic Fever * Avian flu
• Yellow Fever
• Typhoid fever
• Relapsing Fever
• Epidemic typhus
• Malaria
II. Diseases targeted for eradication
and elimination
• Polio/ acute flaccid paralysis
• Dracunculiasis
• Neonatal Tetanus
• Leprosy
III. Other Diseases of public health
importance
• Pneumonia (in children <5 years of age)
• Diarrhea (in children <5 years of age)
• New AIDS cases
• Onchocerciasis
• Sexually Transmitted Infections
• Tuberculosis
• Rabies
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