Transcript Document

Unit 2: Selection of Sentinel
Populations and Sentinel Sites
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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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What You Will Learn
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By the end of this unit you should be able to:
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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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Considerations in Selecting
Sentinel Populations
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Consider the local epidemiology of HIV and
major risk factors
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Consider the state of the epidemic
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Major Risk Behaviours in SubSaharan Africa
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The major mode of transmission in sub-Saharan
Africa is sexual – primarily unprotected heterosexual
intercourse.
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Mother-to-child and transfusion-associated
transmission are less common.
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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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States of the Epidemic
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The state of the epidemic also guides the
selection of sentinel populations.
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An epidemic can be:
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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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Sentinel Surveillance in Different
States of the Epidemic
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In low-level epidemics, sentinel surveillance
should focus on high-risk groups. For
example, commercial sex workers.
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In concentrated epidemics, sentinel
surveillance should include both persons from
high-risk groups and women in ANCs.
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Sentinel Surveillance in Different
States of the Epidemic, Cont.
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In generalised epidemics, sentinel
surveillance should focus primarily on women
in ANCs.
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Since most sub-Saharan African countries
have generalised epidemics, surveillance
should focus on women attending ANCs.
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Table 2.1. Advantages of ANC
Attendees as Sentinel Populations
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ANCs include sexually active women aged 15 to 49.
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ANCs are attended by a large proportion of the adult
female population in many countries.
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HIV testing can be done on an anonymous basis
since blood specimens are taken for other purposes.
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HIV prevalence among pregnant women can be used
to estimate the potential for mother-to-child
transmission of HIV.
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Table 2.1. Advantages of ANC
Attendees as Sentinel
Populations, Cont.
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ANCs are the most common sentinel
surveillance sites in sub-Saharan Africa and
the developing world.
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They therefore provide a basis to compare
districts, countries and regions.
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Table 2.1. Disadvantages of ANC
Attendees as Sentinel Populations
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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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Table 2.1. Disadvantages of ANC
Attendees as Sentinel
Populations, Cont.
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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.
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ANC attendance may vary by gravidity and quality of
care provided.
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ANC-based sentinel surveillance does not directly
measure HIV prevalence in men.
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ANCs may not include or be able to identify women
at highest risk for infection (for example, sex workers).
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Selecting ANC Patients for HIV
Surveillance
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Selection criteria must be standardised.
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Clear inclusion and exclusion criteria must be
established to ensure integrity of results
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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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STI Clinics for HIV Sentinel
Surveillance
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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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Table 2.2. Advantages of STI
Clinic Patients for HIV Sentinel
Surveillance
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HIV testing can be done anonymously with
unlinked results if blood is drawn for serologic
testing for syphilis.
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STI clinics include large numbers of both men
and women.
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Table 2.2. Disadvantages of STI
Clinic Patients for HIV Sentinel
Surveillance
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May not be representative of the population of
all persons with STIs. Many persons self-treat
STIs or seek treatment outside of governmentrun STI clinics.
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Only patients with STI symptoms will seek care.
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Some STIs do not cause symptoms, especially
in women.
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Additional Sentinel Populations
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Patients in other healthcare facilities can
potentially be used as sentinel populations.
For example:
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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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Additional Sentinel Populations,
Cont.
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Members of other high risk populations may
not be seen at a particular clinic. In such
cases, special community-based serosurveys may be needed. Populations include:
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truck drivers
sex workers in brothels or streets
migrant workers
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Table 2.3. Recommendations
for Sentinel Populations in
Sub-Saharan Africa
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First Priority: Pregnant women attending ANCs
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Second Priority: STI clinic attendees
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Third priority: Other populations, for example
sex workers, long-distance truck drivers or male
occupational groups
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Criteria for Site Selection
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Selection of sites for HIV sentinel surveillance
is a balance between:
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including as much of the selected
population as possible
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logistical necessities
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Criteria for Site Selection, Cont.
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Population served: Sites provide services
for selected sentinel populations.
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Blood samples available: Blood is drawn
from patients as part of routine care.
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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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Criteria for Site Selection, Cont.
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Accessibility: Sites are readily accessible to
surveillance staff for data collection or
supervision of data collection.
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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.
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Geographic diversity: Sites are located in
different geographic areas, both in cities and
rural areas.
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Criteria for Site Selection, Cont.
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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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Number and Distribution of
Sentinel Sites
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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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Setting Priorities
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First priority: Include at least one site per
district so that all regions or provinces are
included in the national system
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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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Surveillance with Limited
Resources
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Aim for broad geographic coverage
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Don’t over-stretch resources
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Quality over quantity
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Use of ANC Satellite Sites
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In some countries, ANCs have additional
associated satellite ANCs in their vicinity.
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To pool ANC satellite data with the main site
data, the following criteria must be met:
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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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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.
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Make any changes you want to.
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We will discuss the questions and answers in
a few minutes.
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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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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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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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Answers to Warm Up Questions,
Cont.
4. Since the epidemic in sub-Saharan Africa is
generalised, the ideal sentinel group would
be:
a.
b.
c.
d.
attendees of STI clinics
pregnant women visiting antenatal clinics
factory workers
all of the above
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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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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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Small Group Discussion:
Instructions
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Get into small groups to discuss these
questions.
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Choose a speaker for your group who will
report back to the class.
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Take 15 minutes for this exercise.
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Small Group Reports
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Select one member from your group to
present your answers.
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Discuss with the rest of the class.
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Case Study: Instructions

Try this case study individually.
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We’ll discuss the answers in class.
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Case Study Review

Follow along as we go over the case study in
class.
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Discuss your answers with the rest of the
class.
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Questions, Process Check
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Do you have any questions on the information
we just covered?
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Are you happy with how we worked on Unit 2?
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Do you want to try something different that will
help the group?
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