2. Public Health Surveillance
At the end of this chapter the student is expected to:
Define Public Health surveillance
List out uses of surveillance data
Describe the different types of surveillance
Describe basic activities in surveillance
Explain the Integrated Disease Surveillance and Response system
Identify public health important diseases that are under surveillance
4. Public Health Surveillance
The term surveillance is a French word, which means “Watching
with attention, suspicion and authority”.
Ongoing, systematic collection, analysis, and interpretation of
health-related data essential to the planning, implementation, and
evaluation of public health practice, with the timely dissemination
of these data to those responsible for prevention and control.
Public health surveillance main function is to serve as an “early
warning system” – providing timely information needed for action
(rapid reporting, confirmation, decision making and response).
Public Health Surveillance is
A continuous systematic
dissemination of health data and
Link to public health practice
“Information for Action”
6. What is the difference between survey and surveillance?
• Survey: Making a single observation to measure and record
• The vast majority of surveys done to provide routine
assessment of health and nutritional status in humanitarian
emergencies are cross-sectional.
• A cross-sectional survey is a collection of data at a single
point in time from a specific population.
• Surveillance: Making repeated standardised surveys in
order that change can be detected.
• Surveillance is used to detect change but does not
differentiate between acceptable and unacceptable change.
7. Types of outcomes and indicators measured in a survey
Surveys can gather data to calculate:
• Prevalence: it is the proportion of the population which has a
specific disease at a single point in time.
• Program coverage: it is the proportion of individuals who are
eligible for a program or service who actually receive the
program or service (E.G. Vaccination coverage)
• Incidence rate: is the rate at which new cases of disease occur
in a specified population during a defined time period
8. Surveillance versus survey
• It is relatively cheap (for health
department), can often use
existing systems and health
• Allows monitoring of trends of
disease over time
• Ongoing collection allows to
use enough cases for study
• Quality control may be the
• May not provide
• More in-depth data could be
• More accurate assessment
of true incidence and
• Can identify those which
don’t warrant medical care
• Represents only single point
• Recall bias can be
• It is costly, needs to use by
hiring a trained once.
Purpose /Objectives of surveillance
1. Detect epidemics / outbreaks
2. Predict future epidemics
3. Monitor trends of endemic
4. Monitor health status of a
5. Guide disease prevention and
6. Monitor progress of control
7. Monitor programme performance
8. Evaluate interventions
9. Estimate future disease impact
10. Guide appropriate resource
10. Types of Surveillance
There are three major types of surveillance
1. Passive surveillance
2. Active Surveillance
3. Sentinel surveillance
11. Types of Surveillance…
1. Passive Surveillance
• The health officials sit back, feet up on the desk, and wait for
reports to come in
• That’s a passive system from the perspective of the health
• Routine survey based on passive case detection and on the
routine recording and reporting system.
12. Types of Surveillance…
• Physicians, clinics, laboratories and others required to report
disease are given the appropriate mailing forms and instructions
They expected that they will report all of the cases of
reportable disease that come to their attention.
• The information providers came to the health institutions for
• So more work for the clinicians, less work for the health agency.
13. Types of Surveillance…
Advantages of passive surveillance:
It covers a wide range of problems
It does not require special arrangement
It is relatively cheap
It covers a wider area.
Simpler than Active
Less work for health department
14. Types of Surveillance…
Disadvantages of passive surveillance:
• The information generated is to a large extent unreliable,
incomplete, and inaccurate.
• Most of the time data is not available on time.
• Most of the time, you may not get the kind of information you
• It lacks representativeness as it is mainly from health
• May fail to identify outbreaks
• There is no feedback system i.e. data is analyzed centrally.
15. Types of Surveillance…
2. Active Surveillance
• “Health Department-initiated”
The health officials make periodic (usually weekly) telephone
calls or personal visits to the reporting individuals to obtain the
16. Types of Surveillance…
Techniques for collecting information for Active surveillance:
Sending out a letter describing the situation and asking for
reports, or making a telephone call or visit the facilities to collect
information on cases.
Alerting the public directly, usually through local media
Asking patients of the particular disease if they know anyone else
with the same condition
Conducting a survey of the entire population.
17. Advantages and disadvantages of active
Assure more complete and
Can be used with specific
Can be used for brief periods
Information collected is timely.
It requires good organization.
It is expensive.
It is for short period of time
(lack of continuity).
It is directed towards specific
disease (has limited scope).
18. Types of Surveillance…
Indications of active surveillance:
1. For periodic evaluation of an ongoing program.
2. For programs that have time limit of operation.
E.g. Eradication program
3. When there is occurrence of unusual situations like:
New disease recovery or New mode of transmission.
High risk season/ year is recognized.
Disease is found to affect a new subgroup of the population.
Previously eradicated disease, a particularly severe disease, or
disease of previously low incidence suddenly reappears or occurs
at a high level of incidence. 18
19. Types of Surveillance…
3. Sentinel Surveillance:
Surveillance based on selected population samples.
Pre arranged sample of reporting sources to report all cases.
Sample sources are selected to be those likely to see cases of the
Health officials define homogenous population subgroups and the
regions to be sampled.
Then identify institutions that serve the population subgroups of
interest, and obtain data regarding the condition of interest.
20. Types of Surveillance…
Characteristics of Sentinel Surveillance:
Selected physicians or facilities involved
Specified diseases reported
High quality data collected
Lack of representativeness
Useful for common conditions where
Complete case counting is not important
Public health action is not taken in response to individual
21. Advantages and Disadvantages of sentinel surveillance:
• It is relatively inexpensive.
• It provides a practical
alternative to population based
• It can make productive use of
data collected for other
• The selected population may
not be representative of the
• The use of secondary data may
lead to data of lesser quality and
22. Activities in surveillance
Surveillance involves the following activities:
Data collection and recording
Data compilation, analysis, and interpretation.
Reporting and notification.
Dissemination of findings and providing feedback.
24. Activities in Surveillance
1. Data collection and recording
Each case of a disease in a given area should be recorded.
Data collection could be through:
Record review, interviews, survey using questionnaires, and
Recording for surveillance must be time, person, and place
specific and should include all information necessary for the event.
25. Sources of Surveillance Data
Mortality reports (birth and death certificates…)
Morbidity reports (notifiable disease reports)
Hospital data (discharge diagnoses, surgical logs, hospital
Absenteeism records (school, workplace…)
Laboratory test result reports
Drug utilization records
26. Sources of Surveillance Data…
Adverse drug reaction reports
Police records (especially for injury, alcohol-related crime)
Information on animal reservoirs and vectors (e.g., for rabies...)
Environmental data (hazard surveillance, water and food testing)
Special surveillance systems (e.g., for injury and occupational
27. Activities in surveillance…
2. Data compilation, analysis and interpretation
Data should be collected at each level of the health facility
Each level should make sure that the information collected is
accurate, complete, reliable, and submitted on time.
Analysis of surveillance data involves comparing with some
expected value, identifying difference between them.
28. 2. Data compilation, analysis and interpretation…
First analyzed in terms of time, place, and person using simple
table and graph.
Data should be analyzed at each level of the health delivery
• Observed increases or decreases in disease incidence.
29. 3. Reporting and notification
Reporting is sending the analyzed information to responsible offices
or personalities for decision making.
Any report must be clear and answer questions like what, where,
when, to whom, how and why.
Types of reports:
o Oral: passing information verbally
o Radio or telephone: for special cases like emergency situations
o Written: in normal circumstances
30. 4. Disseminating Data
Data and interpretations should be sent to:
Those who provided reports or other data (e.g., health-care
providers and laboratory directors).
They should also be sent to those who use them for
Managing control programs,
Or other health-related decision-making.
31. Dissemination of Surveillance Data
Public health officials
Clinicians / labs (reporters)
Health agency newsletters
Surveillance summaries / reports
Medical / epidemiologic journal
32. Link to Action
The phrase “information for action” implies that surveillance
systems should be functionally linked with public health programs.
In Ethiopia the MOH, and Regional Health bureaus are responsible
for both surveillance and program action.
33. Link to Action…
Surveillance information can be linked to:
• Outbreak investigation
• Disease control
Vaccination / prophylaxis
Elimination of cause
Interruption of transmission
• Development, targeting of programs (education, risk reduction, etc.)
• Development of policies, regulations
34. Prioritizing Conditions for Surveillance
Ministry of Health interest
Potential for outbreaks
Public perception (concern) of risk
Preventability (e.g., vaccine-
Necessity for immediate public
International requirements (WHO
35. Features of Good Surveillance system
Using a combination of both active and passive surveillance
Timely and comprehensive action taken in response to
Availability of a strong laboratory service for accurate diagnosis
36. Attributes of surveillance
These attributes are:
a) sensitivity – to what extent the system identify all of the events
in the target population?
b) Timeliness – the need for timeliness depends on the public
health urgency of a problem and the types of interventions that
37. 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?
d) Predictive value
• To what extent are reported cases really cases?
38. Attributes of surveillance…
e) Accuracy and completeness of descriptive information
• Forms of reporting health events often include descriptive
personal information, such as demographic characteristics,
clinical pattern of disease, or potential exposures
• Are forms easy to complete?
39. Attributes of surveillance…
• Can it adapt to evolving standards of diagnosis or medical care?
• to what extent are the participants in a surveillance system (those
who report cases, welcome staff to their hospitals or offices,
complete forms, etc.) interested about the system?
41. Integrated Disease Surveillance
and Response (IDSR)
• IDSR is an approach adapted to strengthen national disease
surveillance systems by coordinating and streamlining all
surveillance activities and ensuring timely provision of surveillance
data to all disease prevention and control programs in order to
initiate timely response (intervention).
42. Steps in IDSR
Identify cases of priority diseases and conditions using
standard case definition;
Report all suspected cases or conditions to the next level;
Compile the data, and analyze it for trends, and interpret it;
Investigate and confirm suspected cases and epidemics;
Evaluate and improve the system
44. Diseases and conditions are selected based on one or more of the
Diseases which have high epidemic potential (small pox, severe acute
respiratory syndrome (SARS), viral hemorrhagic fever (VHF), and yellow
Diseases targeted for eradication or elimination- neonatal tetanus (NNT),
Diseases which have a significant public health importance
Diseases that have available effective control and prevention measures
45. Disease Targeted for surveillance
Diseases to be included in surveillance (in Ethiopia):
1. They have a high potential for causing epidemics
2. They have been targeted for eradication or elimination
3. They have significant public health importance (causing many
illnesses and deaths)
4. They can be effectively controlled and prevented.
46. List of Priority Diseases for Surveillance in Ethiopia
2. Diarrhea with blood
6. Viral hemorrhagic fevers
7. Yellow fever
8. Typhoid fever
9. Relapsing fever
B. Diseases targeted for eradication
12.Acute flaccid paralysis (Polio)
13.Dracunculiasis (Guinea worm)
C. Other diseases of public health
16.Pneumonia in children
17.Diarrhea in children
18.New AIDS cases
20.Sexually transmitted diseases
47. Identification of priority diseases …
Identify cases of priority diseases and conditions using Standard
• Case definition:
a set of criteria used to decide if a person has a particular disease, or
if the case can be considered for reporting and investigation.
• Standard case definition:
an agreed up on case definition to be used by everyone with in the
country or across boundaries.
48. Ex. Standard Case Definition
Coryza (runny nose) OR
49. Identification of priority diseases …
Classification of case definition
Confirmed: a case confirmed by appropriate laboratory
Probable: a case with typical clinical features of the
disease without lab confirmation;
Possible/Suspect: a case with few of the typical clinical
50. Advantages of using standard case definition
Cases are identified using same procedures;
Helps improve the detection of cases in time;
It is quicker and cheaper;
Facilitates screening of many sick persons in a short duration of
Efficient in areas where laboratory services are not optimal;
52. Analyze and interpret data on priority diseases
1. Receive data from health facilities:
Two types of surveillance data from reporting health facilities
at the recommended time:
Case-based/line list or other information from suspected
cases of immediately reportable diseases
Weekly and Monthly summary totals of cases and deaths
for the priority diseases.
53. Analyze and interpret data …
2. Prepare to analyze data by time, place, and person
In order to detect epidemics, follow their course, and monitor
public health activities, health staffs need to know:
• How many cases occurred
• Where the cases occurred
• When the cases occurred
• The population most affected
• Risk factors that contributed to transmission of the disease
54. 3. Analyze data by time Cont…
Mesles Outbreak, Kebele 40, Alefataqusa
Woreda, April-May 2006
M A R
4 t h
A P R
A P R
A P R
3 r d
A P R
4 t h
M A Y
M A Y
M A Y
3 r d
Date of Onset of Rash
55. 4. Analyze data by place
Analysis by place provides information that is used to:
Identify the physical features of the land
Understand the population distribution and density of the area
Describe the variety of populations in an area.
Describe environmental factors
Show distances between health units and villages
Spot locations of disease cases and identify populations at
highest risk for transmission of specific diseases.
56. Analyze data by place cont….
Measles Case by Kebele, Metema, March 2006
57. 5. Analyze data by person
Make a table or graph for person analysis
Calculate the percentage of cases occurring within a given age group
Calculate a case fatality rate
58. Analyze data by person
Measles cases by Age, Metema March 2006
0-4 5-9 10-14 15-19 20-24 >25
59. Review the updated charts, tables, graphs and maps
Compare the current situation with previous months, seasons and
Determine if thresholds for action have been reached
7. Summarize and use the analysis results to improve public health
6. Draw conclusions from the analysis
60. Thresholds are markers that indicate something happen or change.
help to answer the question, “When will you take action, and what
will that action be?”
Thresholds are based on information from two different sources:
A local situation analysis
International recommendations from technical and disease control
These guidelines recommend two types of thresholds:
an alert threshold and an action threshold for the diseases
61. a. Alert threshold -further investigation and preparedness activities should
Reporting the suspected problem to the next level,
Reviewing data from the past,
Requesting laboratory confirmation,
Being more alert to new data and trends in the disease or condition,
Investigating the case or condition,
Prepositioning of drugs and supplies,
Mobilization of the needed resources,
Alerting the appropriate disease-specific program manager to a
62. b. Action threshold triggers a definite response.
Possible actions include communicating laboratory confirmation
results to concerned health centers,
Implementing an emergency response such as immunization,
community awareness campaign, or improved infection control
practices in the health care setting etc.