MHD_Epi Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (

Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (Presentation of Anthropology (

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Public Health
Surveillance
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Learning objectives
At the end of this unit students should be able to:
 Describe the concepts of public health surveillance
Describe the approaches and critical elements of public health
surveillance
 Describe the flow of information, function and responsibilities at
the different levels of surveillance
Explain possible limitation of surveillance
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Definition
•Surveillance is derived from a French word ‘SURVEILLER’ meaning
‘to watch over’ which encompasses careful observation and timely
intervention.

•It is a systematic collection, analysis, interpretation & dissemination
of relevant health data for monitoring the occurrence and trends of
disease in human population on an ongoing basis.

•The aim is to prioritize problems and provides “Information for
Action” 178 MHD/Epi for Nursing By Dejene S

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Definition . . . . . . .
•WHO defined as: the continuous (ongoing) scrutiny of the factors
that determine the occurrence and distribution of diseases and
other health related events through a systematic collection of data.
•Surveillance data 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.

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Information for Action
Although surveillance is meant to guide a larger action it also provides the
basis for identifying individuals who need treatment and preventive services.
•Public Health Action
•Priority setting
•Planning, implementing,
and evaluating programs
 investigation
 control
 prevention

Surveillance
Collection
Analysis
Interpretation
Dissemination
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It is relatively cheap, can often use existing systems and health
personnel
Allows monitoring of trends of disease over time
Ongoing collection allows to use enough cases for study
Quality control may be the major problem
May not provide representative data
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Surveillance
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Purpose and uses of Surveillance
To detect sudden change in disease occurrence and distribution.

To learn more about the natural history, clinical spectrum and
epidemiology of a disease.

To follow secular (long-term) trends of a disease

To identify changes in agent, host and environment factors

To detect change in health care practices
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•To facilitate the prevention and control of the diseases
under surveillance
•Estimating Magnitude of the Problem
•Determining geographic distribution of illness
•Early Recognition of Epidemics
•Identifying changes in health practices
•Evaluating public health programs
•Generate hypotheses

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Source of data, who would report etc.
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Types of surveillance
There are three major types of surveillance:
I.Passive Surveillance
II.Active Surveillance
III.Sentinel Surveillance
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Steps in Planning surveillance
1.Establish objectives
2.Develop case definitions
3.Determine data source or data collection mechanisms
4.Develop data collection instruments
5.Field test methods
6.Develop and test analytic approach
7.Ensure use of analysis and interpretation
8.Develop dissemination mechanism

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Disease Targeted for surveillance
Diseases to be included in surveillance should (in Ethiopia):
 Are top causes of high morbidity and mortality
 Their epidemic potential
 Surveillance required internationally (for example, plague,
yellow fever and cholera);
 Availability of effective intervention programs for prevention,
control, eradication or elimination of the diseases (for example,
EPI ).
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List of Priority Diseases in Ethiopia (21)
A.Epidemic-prone diseases
1.Cholera
2.Diarrhea with blood (Shigellosis)
3.Measles
4.Meningitis
5.Plague
6.Viral hemorrhagic fevers
7.Yellow fever
8.Typhoid fever
9.Relapsing fever
10.Epidemic typhus
11.Malaria
B. Diseases targeted for
eradication
12.Acute flaccid paralysis (Polio)
13.Dracunculiasis (Guinea worm)
14.Leprosy
15.Neonatal Tetanus

C. Other diseases of public health
importance
16.Pneumonia in children
17.Diarrhea in children
18.New AIDS cases
19.Onchocerciasis
20.Sexually transmitted diseases
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Limitations of Surveillance Systems
 Under reporting
 Lack of representativeness of reported cases
 Lack of timeliness
 Inconsistency of case-definitions
 Lack and shortage of qualified staff
 Lack of motivation
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Analysis of surveillance data
A.Descriptive analysis: distribution by time,
place and person
– Frequency of events
– Calculate rates- need proper denominator

B.Observe trends: comparison current data
with expected value, identify differences, and
assess the relevance of the difference
– Draw graphs to show long term (secular) trends
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Dissemination of surveillance data
•Disseminate surveillance data to all stakeholders (health
providers, community and decision makers)

•Disseminate report locally, nationally or globally; as necessary as
well timely & regularly

•Disseminate through appropriate media: newsletter or bulletin
(paper or electronic)

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Epidemic
Investigation &
Management
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Learning objectives
At the conclusion of this module, students should be able to:
•Discuss reasons to investigate a possible outbreak
•Describe key steps of outbreak investigations
•Describe some of the methodological approaches in the conduct of an
outbreak investigation
•Apply the three main principles of descriptive epidemiology: person,
place and time
•Understand the role of epidemiology in outbreak investigations

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Levels of Disease Occurrence
•Diseases occur in a community at different levels at a particular
point in time.
I.Expected levels
•Endemic: persistent occurrence of diseases with a low to
moderate level. i.e. more or less at stable level.
•Hyper endemic: Persistently high level of disease occurrence.
•Sporadic: Occasional or irregular occurrence of a disease.
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Levels of Disease . . .
II.Excess of what is expected
•Epidemic: occurrence in excess of the usual frequency in a given area
or among a specific group of people over a particular period of time.
If the number of cases exceeds the expected level on the basis of the
past experience of the particular population, then it is an epidemic.
•Outbreak: Epidemics of shorter duration covering a more limited area.
•Pandemic: An epidemic involving several countries or continents
affecting a large number of people.
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Endemic vs Epidemic
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Epidemics could occur due to
•Recent increase in amount or virulence of the agent
•Recent introduction of the agent into a setting
•Enhanced mode of transmission
•Change in the susceptibility of the host response
•Factors that increase host exposure or involve introduction through
new portals of entry
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Types of epidemics
• Epidemics can be classified according to the method of spread, nature
and length of exposure to the infectious agent, and duration.
A.Common Source Epidemic.
•Occurs as a result of exposure of a group of susceptible persons to a
common source of a pathogen.
•When the exposure is simultaneous, the resulting cases develop
within one incubation period and this is called a point source
epidemic. E.g Food borne epidemic
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Typical Point source epidemics
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Types of epidemics cont.…
•If the exposure to a common source continues over time it will result
in a continuous common source epidemic.
•Range of exposures & IPs widen the peaks of the epidemic curve
E.g. A waterborne outbreak that is spread through a contaminated
community water supply
•The epidemic curve may have a wide peak because of the range of
exposures and the range of incubation periods.
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Continuous Common source epidemics
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Types of epidemics cont.…
B. Propagative/ Progressive Epidemics.
•Infectious agent is transferred from one host to another.
•It can occur through direct and indirect transmissions.
•Propagative spread usually results in an epidemic curve with a
relatively gentle upslope and somewhat steeper tail.
E.g. outbreak of malaria.

•When it is difficult to differentiate the two types of epidemics by the
curve, spot map can help.
•In the propagated epidemics there will be successive generations of
cases.
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Typical Propagated Epidemic Curve
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Types of epidemics cont.…
C. Mixed Epidemics.
•The epidemic begins with a single, common source of an infectious
agent with subsequent propagative spread.
•Many food borne pathogens result in mixed epidemics.

Outbreaks are detected in one of the following ways:
•Through timely analysis of routine surveillance data.
•Report from clinician.
•Report from the community, either from the affected group or
concerned citizen.
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Investigation
•What does it mean by investigation?
• It is the process of recognizing
•.... the cause of the epidemic,
•the source of the cause
•the mode of transmission
•preventive/ control measures .…of an epidemic

•Investigating disease outbreaks is a form of active surveillance.
•The purpose is to determine the specific cause or causes of the
outbreak at the earliest time and to take appropriate measure and
prevent future occurrence.
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Basic Principles of Outbreak Investigation
•Conduct multiple activities simultaneously; run a dynamic process
•Maintain communication with officials, stakeholder and the public
•Apply epidemiological and statistical principles regarding study design
and analysis appropriately
•Record all steps taken in the investigation and all information gathered
•Careful and critical review of the literature should be undertaken
•Investigators must maintain open but critical mind to uncover new
pathogens/transmission means
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Steps in epidemic investigation
There is no hard and fast rule but verification of the diagnosis and establishment
of the existence of an epidemic always deserves early attention
1. Prepare for field work
2. Verify the diagnosis
3. Verify the existence of an epidemic
4. Describe the epidemic with respect to person, place and time
5. Formulate and test hypothesis
6. Search for additional cases
7. Investigate environmental conditions
8. Analyze the data
9. Make a decision on the hypothesis tested
10. Intervention and follow up
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Challenges of Investigating Outbreaks
•Urgency
•Inadequate statistical power due to limited number of cases
•Early media reports may bias responses of persons
•Loss of useful clinical and environmental samples due to late
initiation.
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Management of epidemics
•Management of epidemics requires an urgent and intelligent use of
appropriate measures against the spread of the disease.
•Action to be taken is dependent on the type of the disease as well as
the source of the outbreak.

Measures Directed Against the Reservoir
•Understand the nature of the reservoir
•Domestic animals as reservoir:
•Immunization
•Testing of herds
•Destruction of infected animals
Example: brucellosis and bovine tuberculosis.
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Management of epidemics cont.…
Measures that interrupt the transmission of organisms
•Action to prevent transmission of disease by ingestion:
•Purification of water
•Pasteurization of milk
•Inspection procedures designed to ensure safe food supply.
•Improve housing conditions.
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Measures that reduce host susceptibility
•Active immunization
•Passive immunization
•Chemoprophylaxis
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Thank you!
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