Working Group on Global HIV/AIDS/STI Surveillance
UNAIDS/WHO Working Group on Global
HIV/AIDS and STI Surveillance
UNAIDS/WHO
Surveillance of HIV infection
PREVALENCE: Rate of HIV in a
defined population.
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Period Prevalence: Rate of HIV over a
specified period of time (usually 1 year)
Point Prevalence: Rate of HIV infections in
as short a period as possible (1-2 months)
INCIDENCE: Rate of new HIV infections
over a specified period of time (usually 1
year)
UNAIDS/WHO
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Working Group on Global HIV/AIDS/STI Surveillance
Measuring the prevalence and
incidence of HIV
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To assess the HIV seroprevalence in the population
or in population groups
To monitor trends of HIV infection over time and
place
To provide baseline information for estimates and
future projections of HIV infection and AIDS
To obtain, reinforce or increase the commitment of
policy makers, health workers, local and international
groups and all sectors in AIDS prevention and care
programs
To provide baseline data for appropriate planning of
health and medical services.
UNAIDS/WHO
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Working Group on Global HIV/AIDS/STI Surveillance
Objectives of HIV Surveillance
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Repeated cross-sectional HIV prevalence
studies in selected population groups at
selected sites.
Trends of HIV infection are monitored over
time, by group and by place or site.
Results can be applied confidently only to
the selected population and sites surveyed.
Community(population)-based (e.g.:CSW, IVDU,
MSM)
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Clinic/health facility based (e.g.: ANC, STI, TB)
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
HIV Sentinel Surveillance
UNAIDS/WHO
Monitors trends of infection in a chosen
population
 Can be successfully carried out among high-risk
population groups even when HIV infection in the
general population is very low.
 Can conveniently choose high-risk and low-risk
groups for study and follow-up.
 Less expensive to conduct than general
population surveys.
 The process can become “routine” over a period
of time.
 No participation bias as it is done in an unlinked
anonymous manner.
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Working Group on Global HIV/AIDS/STI Surveillance
Advantages
Results from studies of sentinel groups cannot
be applied to the general population.
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Results from sentinel sites can be considered
representative only of the population utilizing the
services of the sentinel site.
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Results could still be biased due to nonparticipation of sentinel group members (i.e.
selective access to health facilities).
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Disadvantages
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Unlinked anonymous testing using
sample collected for other
purposes in selected health
facilitates
No need for informed consent,
minimises participation bias,
reduced cost.
Services must be available with
sufficient coverage
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Service-based surveillance
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When there are no services available or
blood is regularly collected
Need for informed consent and counselling
if the infected are informed
Potential participation and selection biases
(reduced if saliva or urine are collected)
Potential impact on prevention services
Community involvement and support are
essential
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Community-based surveillance
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STD Clinic Attendees
Commercial Sex Workers (Male and Female)
Male homosexuals and bisexuals
Intravenous
Multiple Blood Recipients
Frequent Travellers
Prisoners
UNAIDS/WHO
Moderate to High Risk of HIV Infection
Working Group on Global HIV/AIDS/STI Surveillance
Potential Sentinel Groups
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Antenatal Clinic Attendees (Pregnant Women)
Voluntary Blood Donors
Health Care Workers
Factory Workers
Persons taking patients to clinics
Newborns
Military/Police Recruits
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Adult Medical Outpatients
TB patients
Participants in surveillance of other diseases
UNAIDS/WHO
Low Risk of HIV Infection
Working Group on Global HIV/AIDS/STI Surveillance
Potential Sentinel Groups
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HIV prevalence in groups representative
of adults of sexually active age in the
general population
Most useful in countries with generalized
epidemics
Useful not only for trend analysis but
also for HIV prevalence estimates
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
HIV Surveillance in Groups
Representing the General Population
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The most common Sentinel Population
Not perfectly representative of all
women and even less of men
Importance of the coverage of ANC
services (>80% in Africa, much less in
Asia and Latin America)
Importance of geographic coverage (All
areas? Urban/rural?)
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Antenatal Clinics (ANC)
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Only pregnant women are tested (HIV
reduces fertility)
Only pregnant women who attend ANC
are tested
Clinics selected may not be
representative
In general terms, ANC data:
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underestimate prevalence in general
female population
overestimate prevalence in the rural
population
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Biases with ANC data
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Importance of younger age groups (1524 yrs)
Consecutive sampling
Time frame, point prevalence
Sample sizes
Socio-demographic variables
testing strategies (Unlinked, voluntary)
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Issues with ANC surveillance
Military recruits
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Blood normally taken Unlinked testing
Recruitment process (random, universal,
voluntary)
Data from only a very limited age group
Screening for occupational health
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Factory workers
Pre-employment screening
Migrant workers
Insurance
UNAIDS/WHO
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Working Group on Global HIV/AIDS/STI Surveillance
Representative male groups
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In theory, the best method to obtain a reliable
estimate of HIV prevalence in the general
population
Normally quite expensive, difficult to conduct
and presenting serious ethical problems
Requires informed consent and counselling
Would be useful from time to time to “calibrate”
regular HIV surveillance (males/females ratio,
urban/rural)
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
HIV sero-surveys in the
general population
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HIV testing can be added to other population-based
studies conducted for other public health objectives
(e.g.: DHS+, HBV, Malaria, anaemia)
Most of the cost and logistics problems already included
in the original study design.
Consistent sampling frame
If appropriate samples are already being collected,
unlinked anonymous testing is still possible.
Potential negative impact on the original objectives of
the study.
Only feasible when and where these studies are
conducted
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
HIV sero-surveys in the
general population
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The main goal is to screen all donations
for blood safety
All population is tested
HIV data is available at no additional
cost
Several biases:
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Selected groups
Self deferral
Multiple donations
HIV+ informed and removed
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Blood donors
Difference between:
Donations= blood bags
UNAIDS/WHO
Donors = individuals
Difference between
Paid donors
Voluntary donors
Working Group on Global HIV/AIDS/STI Surveillance
Blood donors
Replacement donors
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HIV surveillance in sub-populations
whose behaviour may carry a
higher risk than average of HIV
infection
Most useful for concentrated or low
epidemics
Mainly for trend analysis
Limited use for prevalence or
impact assessment
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
HIV Surveillance in
populations at high risk
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Many risk behaviours are highly
stigmatised and some are illegal
Little support for intervention in
these groups
Hard to reach populations
Anonymity or confidentiality is
essential in order to avoid negative
effects on prevention efforts
UNAIDS/WHO

Working Group on Global HIV/AIDS/STI Surveillance
Challenges
TESTING
The application of an HIV antibody test to determine if an individual is
positive or negative for HIV antibody. (Voluntary testing or case
detection).
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SCREENING
The systematic application of HIV antibody test to a population of
apparently healthy people for the purpose of detecting the number of
people (or blood samples) infected with HIV. The primary aim is not to
diagnose HIV infection in a specific person (Blood donors)
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SURVEILLANCE
The collection of information of sufficient accuracy and completeness on
the distribution and spread of infection to be pertinent to the design,
implementation or monitoring of prevention and care activities. Since it
is not feasible to collect information from the total population,
surveillance will have to rely on routine collection of data from sentinel
groups.
UNAIDS/WHO
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Working Group on Global HIV/AIDS/STI Surveillance
Testing, Screening, Surveillance
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VOLUNTARY CONFIDENTIAL TESTING
• Requires informed consent and counselling
• Participation bias is likely
VOLUNTARY ANANYMOUS TESTING
• Requires informed consent and counselling
• Coded sample, only the patient can link the results
• Participation bias is possible
UNLINKED ANANYMOUS TESTING
• Testing of blood collected for other purposes
• No coding, no consent, no counselling required
• Participation bias minimized
MANDATORY TESTING
• Testing required for benefit/service/employment (blood donors)
• Participation bias possible
COMPULSORY TESTING
• Testing is forced on the individual (Unethical)
• Can be anonymous or confidential
• Participation bias may still occur
UNAIDS/WHO
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Working Group on Global HIV/AIDS/STI Surveillance
HIV Testing
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Uses blood which is collected for other purposes (Testing of blood
samples, not individuals)
Ensures anonymity
Avoids the need for informed consent and counselling
Minimizes participation bias
More practical to implement
LIMITATIONS
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Detailed data on high-risk behaviours and other important variables
cannot be obtained
Only groups that have blood taken for other purposes can be studied
HIV-infected persons cannot be contacted and informed about their
status
UNAIDS/WHO
•
Working Group on Global HIV/AIDS/STI Surveillance
Unlinked Anonymous Testing
UNAIDS/WHO
• Sites where blood is already being drawn for other
purposes
• Representative of high-risk and low-risk groups
and/or areas
• Accessible and convenient
• Sufficient number of patients
• Staff willing to participate in surveillance activity
Working Group on Global HIV/AIDS/STI Surveillance
Selection of Sentinel Sites
• Confidence Intervals (CI), a statistical measure of the
precision of the prevalence estimate, should be
calculated for a predetermined degree of accuracy (at
least 90%).
• Sentinel surveillance data should be used to monitor
HIV trends over time. Results of HIV sentinel
surveillance do not provide an accurate estimate of
HIV prevalence in a population or population group.
UNAIDS/WHO
• For meaningful interpretation, results of HIV sentinel
surveillance cannot be aggregated. Prevalence rates
should be calculated separately per site and sentinel
group.
Working Group on Global HIV/AIDS/STI Surveillance
Data Analysis
18
15
• Significant increase in
prevalence from 1991 to 1992
12
9
• Apparent (non-significant)
increase from 1992 to 1993.
6
• Larger CI in 1993 due to small
sample size.
0
3
1991
1992
1993
Number tested
412
413
227
Number HIV+
24
56
34
HIV Prevalence
5.8
13.8
14.9
90% C.I.
1.9
2.8
4
UNAIDS/WHO
• Trends in HIV prevalence in
STD patients in one sentinel
site with 90% CI.
Working Group on Global HIV/AIDS/STI Surveillance
Confidence Intervals