recent infection with HIV and estimation

Accuracy of serological assays for detection of recent infection with HIV and estimation of population incidence: a systematic review.

The authors systematically reviewed the accuracy of serological tests for recent infections with HIV that have become widely used for measuring population patterns incidence of HIV. Across 13 different assays, sensitivity to detect recent infections ranged from 42-100% (median 89%). Specificity for detecting established infections was between 49.5% and 100% (median 86.8%) and was higher for infections of durations longer than 1 year (median 98%, range 31.5-100.0). For four different assays, comparisons were made between assay-derived population incidence estimates and a reference incidence estimate. The median percentage difference between the assay-derived incidence and reference incidence was 26.0%. Serological assays have reasonable sensitivity for the detection of recent infection with HIV, but are vulnerable to misclassifying established infections as recent-potentially leading to biases in incidence estimates. This conclusion is highly qualified by the apparent absence of a standardised approach to assay evaluation. There is an urgent need for an internationally agreed framework for evaluating and comparing these tests.

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Editors’ note: Determining HIV incidence directly by measuring seroconversion and thereby monitoring HIV transmission is key to both assessing the need for and establishing the effectiveness of HIV prevention programmes. This extensive review confirms that the development of reliable and valid tests to detect recent infection is a public health priority. To date virtually all the assays that have been developed involve subtype B virus (clade C is the most common worldwide) and have been plagued by false positive results due to longstanding infections or an increasing duration of antiretroviral treatment. Given that HIV incidence reduction is a foundation of both national and international HIV commitments, it is urgent that a standardised approach to assay validation be developed and implemented.

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Estimates of HIV incidence from household-based prevalence surveys.

Hallett TB, Stover J, Mishra V, Ghys PD, Gregson S, Boerma T. AIDS. 2010 ;24:147-52.

This study set out to estimate HIV incidence in the general population in countries where there have been two recent household-based HIV prevalence surveys (the Dominican Republic, Mali, Niger, Tanzania, and Zambia). Hallett et al applied a validated method to estimate HIV incidence using HIV prevalence measurement in two surveys. The authors estimate incidence among men and women aged 15-44 years to be: 0.5/1000 person-years at risk in the Dominican Republic 2002-2007, 1.1/1000 in Mali 2001-2006, 0.6/1000 in Niger 2002-2006, 3.4/1000 in Tanzania 2004-2008, and 11.2/1000 in Zambia 2002-2007. The groups most at risk in these epidemics are typically 15-24-year-old women and 25-39-year-old men. Incidence appears to have declined in recent years in all countries, but only significantly among men in the Dominican Republic and Tanzania and women in Zambia. Using prevalence measurements to estimate incidence reveals the current level and age distribution of new infections and the trajectory of the HIV epidemic. This information is more useful than prevalence data alone and should be used to help determine priorities for interventions.

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Editors’ note: Why have we not been estimating HIV incidence from household surveys? This straightforward method of comparing current age cohorts with their representation in a previous survey includes adjustments for deaths and the numbers of people on treatment by age group. The gold standard, a cohort incidence study, is too expensive and the cohorts in question may not represent the national population anyway. Just as trends in HIV prevalence among pregnant women aged 15 to 24 years have been a proxy for HIV incidence, so too can this approach detect changes in HIV incidence, but at a variety of ages .