Methodological Challenges in Biomedical HIV Prevention Trials (2008) / Chapter Skim
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8 Estimating HIV Incidence
8 Estimating HIV Incidence
Pages 175-185
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From page 175... ...
Although HIV prevalence -- the proportion of people who are infected at a single point in time -- can be measured through cross-sectional studies, estimating HIV incidence, or the number of people who become infected with HIV over a given amount of time, is much more difficult, because HIV infection is a silent event. There are three major approaches for estimating HIV incidence for the purpose of designing a trial: direct longitudinal follow-up of populations; biomarkers that indicate recent infection on cross 175
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From page 176... ...
However, although surrogate markers and behavioral risk factors can be used to target further investigations of HIV incidence, they cannot provide quantitative estimates of HIV incidence, and they should not substitute for direct measurement of HIV incidence in trial design. DIRECT LONGITUDINAL FOLLOW-UP: COHORT STUDIES A method often used to estimate HIV incidence is a prospective cohort study, in which a well-defined cohort of at-risk, uninfected individuals is followed over time and serially tested for HIV infection to identify seroconversions.
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From page 177... ...
BIOMARKERS OF RECENT INFECTION A second approach that has been investigated since the 1990s entails using laboratory-based assays, which can distinguish recent from longstanding HIV infections based on virologic or immunologic markers of HIV disease progression, to estimate population-level HIV incidence (Brookmeyer and Quinn, 1995) . The development of an accurate biomarker of recent infection that could be used to estimate incidence would be a major advance.
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From page 178... ...
Estimating incidence using viral tests involves a two-stage algorithm that first tests all samples for antibodies and then tests all antibody negative samples with a viral preseroconversion test,
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From page 179... ...
Antibody Tests Antibody tests can be used to estimate incidence by distinguishing antibody responses in recently infected individuals from antibody responses in those with established infection. The two most commonly used antibody based methods are: the Serological Testing Algorithm for Recent HIV Seroconversion (STARHS)
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From page 180... ...
An alternative approach to enhancing the performance of the BED assay is to improve the accuracy of the mean window period in Equation In Sakarovitch et al., 2007, most of the specimens that were misclassified as incident cases were from individuals infected longer than 6 months but less than 1 year. The BED-CEIA detects levels of anti-HIV IgG relative to total IgG and is based on the observation that the ratio of anti-HIV IgG to total IgG increases with time after HIV infection.
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From page 181... ...
McDougal and colleagues (2006) applied such a sequential testing algorithm -- using the BED assay followed by the avidity assay -- to specimens obtained from a longitudinal cohort study, the AIDSVAX B/B vaccine trial, which had a direct measure of HIV incidence.
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From page 182... ...
Overall, while incidence estimates derived from mathematical models can be particularly useful in tracking changes in the HIV epidemic at the population level (partly because the relative change rather than the absolute estimate is important) , such models do not have enough precision to estimate HIV incidence for a prevention trial.
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From page 183... ...
This will require recruiting subjects from countries with low-level, concentrated, and generalized epidemics during the pre seroconversion period and following them for several years. Recommendation 8-3: Although further validation studies are being conducted to examine concerns that the STAHRS and BED tests may produce biased estimates of HIV incidence, investigators should not rely solely at this time on these or other biomarker assays of recent infection to estimate HIV incidence for the specific purpose of design ing a prevention trial.
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From page 184... ...
2002. Real-time, universal screening for acute HIV infection in a routine HIV counseling and testing population.
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From page 185... ...
2003. Methods and procedures for estimating HIV/AIDS and its impact: The UNAIDS/WHO estimates for the end of 2001.
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