1. Unit 2: Selection of Sentinel Populations and Sentinel Sites
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2. Warm Up Questions: Instructions
Take five minutes now to try the Unit 2 warm up questions in your manual.
Please do not compare answers with other participants.
Your answers will not be collected or graded.
We will review your answers at the end of the unit.
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3. What You Will Learn By the end of this unit you should be able to:
Identify the primary way the HIV is transmitted in sub-Saharan Africa
list the considerations for selecting sentinel populations
identify specific groups that would be ideal sentinel populations
define criteria for selection of sentinel sites
Identify sites in your district that fit the selection criteria
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4. Considerations in Selecting Sentinel Populations
Consider the local epidemiology of HIV and major risk factors
Consider the state of the epidemic
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5. Major Risk Behaviours in Sub-Saharan Africa
The major mode of transmission in sub-Saharan Africa is sexual – primarily unprotected heterosexual intercourse.
Mother-to-child and transfusion-associated transmission are less common.
Male-male sexual behaviour and injection drug use are little studied in the region, but are less common than heterosexual transmission.
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6. States of the Epidemic
The state of the epidemic also guides the selection of sentinel populations.
An epidemic can be:
Low-level - HIV prevalence has never been above 5% in any high-risk population
Concentrated – HIV prevalence is consistently higher than 5% in at least one high-risk population
Generalised – HIV prevalence among women in ANCs in urban areas is consistently above 1%
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7. Sentinel Surveillance in Different States of the Epidemic
In low-level epidemics, sentinel surveillance should focus on high-risk groups. For example, commercial sex workers.
In concentrated epidemics, sentinel surveillance should include both persons from high-risk groups and women in ANCs.
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8. Sentinel Surveillance in Different States of the Epidemic, Cont.
In generalised epidemics, sentinel surveillance should focus primarily on women in ANCs.
Since most sub-Saharan African countries have generalised epidemics, surveillance should focus on women attending ANCs.
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9. Table 2.1. Advantages of ANC Attendees as Sentinel Populations
ANCs include sexually active women aged 15 to 49.
ANCs are attended by a large proportion of the adult female population in many countries.
HIV testing can be done on an anonymous basis since blood specimens are taken for other purposes.
HIV prevalence among pregnant women can be used to estimate the potential for mother-to-child transmission of HIV.
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10. Table 2.1. Advantages of ANC Attendees as Sentinel Populations, Cont.
ANCs are the most common sentinel surveillance sites in sub-Saharan Africa and the developing world.
They therefore provide a basis to compare districts, countries and regions.
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11. Table 2.1. Disadvantages of ANC Attendees as Sentinel Populations
ANCs do not include infertile women, women who have abortions and women on contraceptives.
HIV may decrease fertility and women’s desire for children, so HIV+ women will be under-represented.
HIV prevalence in pregnant women aged 15 to 19 is likely an overestimate of the general population since many 15- to 19-year-olds may be sexually naïve.
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12. Table 2.1. Disadvantages of ANC Attendees as Sentinel Populations, Cont.
ANCS may underestimate HIV prevalence in older age groups since they are less likely to get pregnant or come to clinics if they are pregnant.
ANC attendance may vary by gravidity and quality of care provided.
ANC-based sentinel surveillance does not directly measure HIV prevalence in men.
ANCs may not include or be able to identify women at highest risk for infection (for example, sex workers).
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13. Selecting ANC Patients for HIV Surveillance
Selection criteria must be standardised.
Clear inclusion and exclusion criteria must be established to ensure integrity of results
For example, to minimise multiple sampling of the same women attending an ANC, include only women who are attending the ANC for the current pregnancy for the first time.
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14. STI Clinics for HIV Sentinel Surveillance
STI clinic patients are an easily identifiable and readily accessible group at high risk for acquiring HIV infection through sexual intercourse.
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15. Table 2.2. Advantages of STI Clinic Patients for HIV Sentinel Surveillance
HIV testing can be done anonymously with unlinked results if blood is drawn for serologic testing for syphilis.
STI clinics include large numbers of both men and women.
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16. Table 2.2. Disadvantages of STI Clinic Patients for HIV Sentinel Surveillance
May not be representative of the population of all persons with STIs. Many persons self-treat STIs or seek treatment outside of government-run STI clinics.
Only patients with STI symptoms will seek care.
Some STIs do not cause symptoms, especially in women.
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17. Additional Sentinel Populations
Patients in other healthcare facilities can potentially be used as sentinel populations. For example:
Tuberculosis (TB) clinics
Hospital wards and clinics providing healthcare to refugees or other high-risk groups
Industrial medicine clinics for factory workers, miners or plantation workers
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18. Additional Sentinel Populations, Cont.
Members of other high risk populations may not be seen at a particular clinic. In such cases, special community-based sero-surveys may be needed. Populations include:
truck drivers
sex workers in brothels or streets
migrant workers
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19. Table 2.3. Recommendations for Sentinel Populations in Sub-Saharan Africa
First Priority: Pregnant women attending ANCs
Second Priority: STI clinic attendees
Third priority: Other populations, for example sex workers, long-distance truck drivers or male occupational groups
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20. Criteria for Site Selection
Selection of sites for HIV sentinel surveillance is a balance between:
including as much of the selected population as possible
logistical necessities
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21. Criteria for Site Selection, Cont.
Population served: Sites provide services for selected sentinel populations.
Blood samples available: Blood is drawn from patients as part of routine care.
Laboratory access: A reliable laboratory is available on-site or nearby to perform routine laboratory tests. Alternatively, reliable roads and transport options exist to send specimens to reference laboratory.
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22. Criteria for Site Selection, Cont.
Accessibility: Sites are readily accessible to surveillance staff for data collection or supervision of data collection.
Size of client base: Sites provide services to a large enough number of persons so that target sample size can be obtained within sampling period.
Geographic diversity: Sites are located in different geographic areas, both in cities and rural areas.
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23. Criteria for Site Selection, Cont.
Resources: Needed resources – human, laboratory, transport – can be mobilised.
Staff acceptance: On-site staff understand the need for HIV sentinel surveillance, are willing to implement activities and are open to training and supervision.
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24. Number and Distribution of Sentinel Sites
Number and distribution of sites is usually decided on a national level. Ideally, sentinel sites will:
Represent each district
Reflect the country-wide epidemic
Include both urban and rural areas
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25. Setting Priorities
First priority: Include at least one site per district so that all regions or provinces are included in the national system
Second priority: Include additional sites in particular districts because sexual behaviour and determinants for HIV transmission may not be uniformly distributed
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26. Surveillance with Limited Resources
Aim for broad geographic coverage
Don’t over-stretch resources
Quality over quantity
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27. Use of ANC Satellite Sites
In some countries, ANCs have additional associated satellite ANCs in their vicinity.
To pool ANC satellite data with the main site data, the following criteria must be met:
The satellite sites’ catchment populations should be similar to those of the main site.
The satellite sites’ epidemic should be similar to the main site.
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28. Warm Up Review
Take a few minutes now to look back at your answers to the warm up questions at the beginning of the unit.
Make any changes you want to.
We will discuss the questions and answers in a few minutes.
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29. Answers to Warm Up Questions
1. True or false? In generalised HIV epidemics, surveillance activities should be focused on groups that exhibit high-risk behaviours. False
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30. Answers to Warm Up Questions, Cont.
2. Which of the following is a key consideration for selecting a sentinel population for HIV surveillance purposes?
a. the local epidemiology of HIV and the major risk factors that drive HIV transmission
b. the state of the epidemic
c. both of the above
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31. Answers to Warm Up Questions, Cont.
3. True or false? In a concentrated epidemic, voluntary blood donors would be an ideal potential sentinel population. False
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32. Answers to Warm Up Questions, Cont.
4. Since the epidemic in sub-Saharan Africa is generalised, the ideal sentinel group would be:
a. attendees of STI clinics
b. pregnant women visiting antenatal clinics
c. factory workers
d. all of the above
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33. Answers to Warm Up Questions, Cont.
5. True or false? When selecting sites for sentinel surveillance, the sites should be located in geographically diverse areas, both inside and outside major cities and towns. True
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34. Answers to Warm Up Questions, Cont.
6. True or false? Provincial or district level staff should make decisions about the number and location of sentinel sites. False
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35. Small Group Discussion: Instructions
Get into small groups to discuss these questions.
Choose a speaker for your group who will report back to the class.
Take 15 minutes for this exercise.
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36. Small Group Reports
Select one member from your group to present your answers.
Discuss with the rest of the class.
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37. Case Study: Instructions
Try this case study individually.
We’ll discuss the answers in class.
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38. Case Study Review Follow along as we go over the case study in class.
Discuss your answers with the rest of the class.
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39. Questions, Process Check
Do you have any questions on the information we just covered?
Are you happy with how we worked on Unit 2?
Do you want to try something different that will help the group?
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