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1. Epidemiological Surveillance

2. Learning Objectives
• At the end of this unit the student is expected to:
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- Define surveillance
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- Describe the types of surveillance
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- Discuss the activities of surveillance
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- Identify public health important diseases that are under
surveillance in Ethiopia
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Surveillance
Definition :
• Surveillance is defined as the continuous (ongoing) study of the
factors that determine the occurrence and distribution of
diseases and other health related events through a systematic
collection of data.
• Epidemiologic Surveillance is the systematic collection, analysis,
interpretation and dissemination of health data in an ongoing
basis.

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Purpose of surveillance
 Early detection of problems (“early warning system”)
E.g. Epidemic
 Provide scientific baseline data and information for priority
setting, planning, implementing and evaluating disease control
programs (Provides “Information for Action” )
 Define the magnitude and distribution of diseases by time, person
and place dimension.
 Identification of seasonal and long-term trends of disease in the
area.

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Types of surveillance
The two common types of surveillance are:
1. Passive Surveillance
2. Active Surveillance

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1. Passive surveillance
• Passive surveillance is defined as a mechanism of survey based
on the routine recording and reporting system.
• The information provider comes to the health institutions for
help, be it medical or other preventive and promotive health
services.
• It involves collection of data as part of routine provision of health
services.

7. Passive surveillance…
Advantages:
– covers a wide range of problems and area
– does not require special arrangement
– is relatively cheap
Disadvantages
• The information is to a large extent unreliable, incomplete and
inaccurate
• Lacks timeliness
• Desired information may not be there
• Lacks representativeness
• No feed back system
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2. Active surveillance
• Active surveillance is defined as a method of data collection
usually on a specific disease, for relatively limited period of time
through:
– House-to-house surveys or
– Mobilizing communities to some central point where data can
be collected.
Example: Investigation of out-breaks

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Active surveillance…
The advantages of active surveillance
ƒ1. the collected data is complete and accurate
ƒ2. information collected is timely.
The disadvantages of active surveillance
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1. it requires good organization,
ƒ2. it is expensive
ƒ3. it requires skilled human power
ƒ4. it is for short period of time(not a continuous process)
ƒ5. it is directed towards specific disease conditions

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Conditions in which active surveillance is appropriate
Active surveillance is appropriate for:-
• For periodic evaluation of an ongoing program
• For programs with limited time of operation such as
eradication program
• In unusual situations such as:
ƒ- New disease discovery
ƒ- New mode of transmission
ƒ- When a previously eradicated disease reappears.

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Activities in Surveillance
The different activities carried out under surveillance are:
1. Data collection and recording
2. Data compilation, analysis and interpretation
3. Reporting and notification
4. Dissemination of information

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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
- Availability of a strong laboratory service for accurate
diagnoses of cases

13. Criteria for identifying disease for surveillance
 Frequency
– Incidence
– Prevalence
 Severity
– Case fatality ratio
– Hospitalization rate
– Disability rate
 Cost
 Preventability
 Communicability
 Public Interest
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I. Immediately Reportable Diseases II. Weekly Reportable Diseases
1 Acute Flaccid Paralysis 14 Dysentery
2 Anthrax 15 Malaria
3 Avian Human Influenza 16 Meningitis
4 Cholera 17 Relapsing fever
5 Dracunculiasis / Guinea worm 18 Typhoid fever
6 Measles 19 Typhus
7 Neonatal Tetanus 20 Malnutrition
8 Pandemic Influenza A (H1N1)
9 Rabies
10 Smallpox
11 Severe Acute Respiratory
Syndrome (SARS)
12 Viral Hemorrhagic Fever (VHF)
13 Yellow fever
FMOH of Ethiopia identified 20 diseases and health events
to be reported immediately and weekly at national level

15. Surveillance Vs survey
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16. Surveillance Vs survey
Surveillance
• Relatively cheap – can often
use existing systems and
health personnel
• Allows monitoring of trends
of disease over time
• Ongoing collection produce
enough cases for study
But…
• Quality control may be the
major problem
• May not provide
representative data
survey
• More in-depth data could be
collected
• More accurate assessment of
true incidence and prevalence
• Can identify those which don’t
warrant medical care
But…
• Costly
• Represents only single point in
time- does not show changes
over time
• Recall bias can be introduced
(retrospective data)
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