HIV This Week

A Tale of Two Countries: HIV Among Core Groups in Togo. Sobéla F, Pépin J, Gbéléou S, Banla AK, Pitche VP, Adom W, Sodji D, Frost E, Deslandes S, Labbé AC. J Acquir Immune Defic Syndr 2009 51: 216-23.

Sobéla and colleagues set out to describe the epidemiology of HIV among core groups in Togo. The authors enumerated sex workers and conducted cross-sectional surveys of sex workers and their clients in 2003 in Lomé and in 2005 in the whole country. Sex work was concentrated in Lomé, which comprised 15% of the population, but 52% of the 5397 SWs enumerated in Togo in 2005 and 68% of the estimated 101,376 men who had bought sex in the year before the 2005 survey. HIV prevalence among sex workers was highest in Lomé (45.4% in 2005) and progressively decreased from south to north. A similar geographical pattern was seen for clients (8.3% were HIV infected in Lomé in 2005) and had already been reported for pregnant women. In Lomé, the population attributable fraction of prevalent cases of HIV acquired during transactional sex was estimated at 32%; in the rest of the country, this was only 2%. This is the first study quantifying sex work at a national level in Africa. Variations in HIV prevalence within Togo, with a north-south gradient among sex workers, their clients, and pregnant women, may to a large extent reflect the concentration of the sex trade within Lomé. Prostitution played only a modest a role in HIV dynamics outside Lomé.

Abstract: 1

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Editors’ note : This unique national study used the anonymous linked method of HIV surveillance by which sex workers and clients who wished to learn their HIV test results returned to the clinic presenting the envelope with their study number they had been given at the time that their fingerprick blood specimen was taken. The authors attribute the relatively low population attributable fraction (the proportion of incidence that is due to sex work-related transmission) in Lomé of 32%, compared to 84% in Accra and 76% in Cotonou, to the sustained NGO-implemented programme (Forces et Action pour le Mieux-Être de la Mère et de l’Enfant) that has ensured condom availability in sex work environments since the early 1990s.

Refusal bias in HIV prevalence estimates from nationally representative seroprevalence surveys. Reniers G, Eaton J. Aids. 2009; 23 : 621-9.

Reniers and Eaton set out to assess the relationship between prior knowledge of one’s HIV status and the likelihood to refuse HIV testing in population-based surveys and explore its potential for producing bias in HIV prevalence estimates. Using longitudinal survey data from Malawi, the authors estimate the relationship between prior knowledge of HIV-positive status and subsequent refusal of an HIV test. The authors use that parameter to develop a heuristic model of refusal bias that is applied to six Demographic and Health Surveys, in which refusal by HIV status is not observed. The model only adjusts for refusal bias conditional on a completed interview. Ecologically, HIV prevalence, prior testing rates and refusal for HIV testing are highly correlated. Malawian data further suggest that amongst individuals who know their status, HIV-positive individuals are 4.62 (95% confidence interval, 2.60-8.21) times more likely to refuse testing than HIV-negative ones. On the basis of that parameter and other inputs from the Demographic and Health Surveys, the model predicts downward bias in national HIV prevalence estimates ranging from 1.5% (95% confidence interval, 0.7-2.9) for Senegal to 13.3% (95% confidence interval, 7.2-19.6) for Malawi. In absolute terms, bias in HIV prevalence estimates is negligible for Senegal but 1.6 (95% confidence interval, 0.8-2.3) percentage points for Malawi. Downward bias is more severe in urban populations. Because refusal rates are higher in men, seroprevalence surveys also tend to overestimate the female-to-male ratio of infections. Prior knowledge of HIV status informs decisions to participate in seroprevalence surveys. Informed refusals may produce bias in estimates of HIV prevalence and the sex ratio of infections.

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Editors’ note : The results of nationally representative household surveys that include HIV testing are used to adjust for the biases of antenatal care sentinel surveillance estimates to create revised national HIV prevalence estimates in many countries in sub-Saharan Africa. This model suggests that the results of household surveys in some high HIV prevalence urban areas with high HIV testing coverage may underestimate true HIV prevalence. This would be due to the possibility that those refusing to participate, who are more likely to be men, may be more likely to know that they are HIV-positive already. No systematic adjustment for this is warranted at this time but countries should be aware of this potential bias and consider ways to both encourage participation by all those who are sampled and to study the potential for this bias to be influencing estimates in their own settings.