1. Surveillance of HIV infection
UNAIDS/WHO Working Group on Global HIV/AIDS and STI Surveillance
The slides presents the basic principles and definitions for HIV surveillance,
possible strategies with its advantages and disadvantages and provide some
advice in sentinel groups, sites and samples sizes.

2. Measuring the prevalence and incidence of HIV
PREVALENCE: Rate of HIV in a defined population.
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)
Basic epidemiological concepts of Prevalence and Incidence.

3. Objectives of HIV Surveillance
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.
To stress the principle of collecting data for action

4. HIV Sentinel Surveillance
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)
Clinic/health facility based (e.g.: ANC, STI, TB)
Main features of HIV sentinel surveillance

5. Advantages 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.
To stress the advantages of sentinel surveillance over population studies.
It needs to be balanced available resources with information needs. Cost
efficient and effective approach

6. Disadvantages
Results from studies of sentinel groups cannot be applied to the general population.
Results from sentinel sites can be considered representative only of the population utilizing the services of the sentinel site.
Results could still be biased due to non-participation of sentinel group members (i.e. selective access to health facilities).
When interpreting data from sentinel studies we should be aware of
its limitations, therefore have to be careful with extrapolations of results.
Female Vs Male, age groups, fertility rates, attendance to the clinic.

7. Service-based surveillance
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
Principles of sentinel surveillance in a health service to minimise bias using
the unlinked anonymous approach. However, such services must be available
with sufficient coverage of the population under study.

8. Community-based surveillance
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
Principles of intervention in population or community studies. While more
difficult and complex to conduit, community-based studies are often the
only options where specific facilities or services are not available.
Often these studies take advantage of existing intervention projects.

9. Potential Sentinel Groups
Moderate to High Risk of HIV Infection
• STD Clinic Attendees
• Commercial Sex Workers (Male and Female)
• Male homosexuals and bisexuals
• Intravenous
• Multiple Blood Recipients
• Frequent Travellers
• Prisoners
Groups should be choosen according to the state of the epidemic and possible
risk groups in a country.
Mode of transmission on AIDS cases can provide additional information.
There is need to balance feasibility and cost of surveillance for the groups.

10. Potential Sentinel Groups
Low Risk of HIV Infection
• Antenatal Clinic Attendees (Pregnant Women)
• Voluntary Blood Donors
• Health Care Workers
• Factory Workers
• Persons taking patients to clinics
• Newborns
• Military/Police Recruits
• Adult Medical Outpatients
• TB patients
• Participants in surveillance of other diseases
This groups are considered low risk and should not be a sentinel group in
low or concentrated epidemics, though information available e.g.: blood donors
should be used to understand the dynamics of HIV.

11. HIV Surveillance in Groups Representing the General Population
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
Often the best group that can be used as a “proxy” for the general
adult population is pregnant women attending health
services.

12. Antenatal Clinics (ANC)
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?)
ANC as a good representative group for general population in generalised
epidemics but still has its limitations: coverage, fertility trends, age
distribution, access to services. But it can provide reliable data for trends
if consistency is maintain

13. Biases with ANC data
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:
underestimate prevalence in general female population
overestimate prevalence in the rural population
Several biases complicate the use of ANC data as “representative” of the
general population and must be taken into consideration when
analyzing the data.

14. Issues with ANC surveillance
Importance of younger age groups (15-24 yrs)
Consecutive sampling
Time frame, point prevalence
Sample sizes
Socio-demographic variables
testing strategies (Unlinked, voluntary)
Main steps on surveillance using ANC clinics

15. Representative male groups
Military recruits
Blood normally taken Unlinked testing
Recruitment process (random, universal, voluntary)
Data from only a very limited age group
Screening for occupational health
Factory workers
Pre-employment screening
Migrant workers
Insurance
Groups that can represent the adult male populations are more difficult to
reach. These are some options for HIV prevalence studies in men.

16. HIV sero-surveys in the general population
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)
HIV sero-prevalence surveys in a random sample of the general adult
population are in theory the best method to obtain reliable estimates of
HIV prevalence. However their complexity and costs limit the utilization.

17. HIV sero-surveys in the general population
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.
An alternative to conducting costly HIV seroprevalence studies in the
general population is to use existing population-based studies for other
diseases or health conditions and add HIV testing to it. While reducing costs,
these studies may still prove difficult to conduct and raise important
ethical considerations.
Potential negative impact on the original objectives of the study.
Only feasible when and where these studies are conducted

18. Blood donors 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:
Selected groups
Self deferral
Multiple donations
HIV+ informed and removed
To highlight the use of available data in many forms like blood donors. Regular
data, good coverage, general population. It is important to know where the
donors come from., age and sex distribution. Most useful for low and
concentrated epidemics.

19. Blood donors Difference between: Difference between
Donors = individuals
Donations= blood bags
Difference between
For surveillance purposes, it is essential to differentiate HIV prevalence in
blood donations (blood bags tested) and HIV prevalence in blood donors
(individuals donating blood) since many voluntary donors may donate more
once per year.
It is also important to distinguish between “paid donors”, voluntary
non-remunerated donors and “family replacement” donors. True family
replacement donors provide the best proxy for the general adult population.
Paid donors
Voluntary donors
Replacement donors

20. HIV Surveillance in populations at high risk
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
To stress the need to survey high risk groups in low level and concentrated
epidemics. It need to be innovative approach as these groups are hard to each;
use of NGO as an entry point.

21. Challenges
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
Difficulties with these groups. Useful if studies are together with prevention
and care activities

22. Testing, Screening, Surveillance
The application of an HIV antibody test to determine if an individual is positive or negative for HIV antibody. (Voluntary testing or case detection).
• 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)
• 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.
Stress different concepts of testing, screening and surveillance

23. HIV Testing • VOLUNTARY CONFIDENTIAL TESTING
• Requires informed consent and counselling
• Participation bias is likely
• VOLUNTARY ANANYMOUS TESTING
• 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
Principles and types of HIV testing: for HIV surveillance unlinked
anonymous is the best as it has less bias.

24. Unlinked Anonymous Testing
• 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
• 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
Principles of HIV unlinked anonymous testing

25. Selection of Sentinel Sites
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
Minimum criteria used to select sentinel sites for HIV surveillance: access to
services, staff collaboration, enough clients, not overload the health services.

26. Data Analysis
For meaningful interpretation, results of HIV sentinel surveillance cannot be aggregated. Prevalence rates should be calculated separately per site and sentinel group.
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.
Stress the limit use of statistical analysis as is sentinel surveillance, not
random sample therefore the number of statistical analysis is more limited,
but minimum as CI possible. Importance to monitor trends

27. Confidence Intervals
Trends in HIV prevalence in STD patients in one sentinel site with 90% CI.
Significant increase in prevalence from 1991 to 1992
Apparent (non-significant) increase from 1992 to 1993.
Larger CI in 1993 due to small sample size.
Example of CI and the effects of sample size. Smaller N implies bigger CI
, therefore lees reliable data.
Stress minimum sample sizes