Editor’s notes: A key challenge for epidemiological research involving key populations is to find a representative sample. Whereas national surveys such as demographic health surveys (DHS) and PHIA can use the total population to create a sampling frame from which to draw individuals at random, researchers interested in key populations have to use a range of methods, all of which have limitations as well as strengths. Internet and app-based surveys may accrue large numbers, but may have significant biases in terms of who chooses to answer such questionnaires. Venue-based sampling allows data to be collected from people who happen to be at the venue at the same time as the researchers. Respondent driven sampling has become increasingly popular as a method to reach individuals that might otherwise be hard to include in studies. Increasingly sophisticated statistical methods have been developed to adjust estimates, and in particular their precision, according to characteristics of respondents found in the sample.
Malawi, Wirtz et al. point out that many respondent driven samples of key populations, such as that from Hladik et al., are only able to collect data from one particular city or region, and that this can lead to misinterpretation if the results are generalized to whole countries. The authors conducted a large study of gay men and men who have sex with men in seven different communities across Malawi. They found considerable heterogeneity leading to an overall estimate that the risk of HIV was approximately twice as high in gay men and men who have sex with men as in the general population of men of the same age. The study managed to enrol a total of almost 2500 men through respondent driven sampling in the different districts. However, this was at the expense of having to collect data over a considerable time period, with the study team moving from district to district. As the authors acknowledge, the risk is that data collected in the most recent time period may not be equivalent to data collected four years previously. The authors did find that the highest rates of HIV among gay men and men who have sex with men were not always where they have been presumed to be. In particular tourist areas and some rural areas had higher rates than some of the cities that are usually the focus of key populations programmes. Once again, the finding that so few gay men and men who have sex with men knew their status and were linked to treatment may not be surprising but is still shocking. Only 1% of men found to be positive reported that they were aware of their status. The authors point out the tension between public health and policy in a country where homosexuality is criminalized. If HIV is to be prevented, this tension will need to be resolved.
Geographical disparities in HIV prevalence and care among men who have sex with men in Malawi: results from a multisite cross-sectional survey.
Wirtz AL, Trapence G, Kamba D, Gama V, Chalera R, Jumbe V, Kumwenda R, Mangochi M, Helleringer S, Beyrer C, Baral S. Lancet HIV. 2017 Jun;4(6):e260-e269. doi: 10.1016/S2352-3018(17)30042-5. Epub 2017 Feb 28.
Background: Epidemiological assessment of geographical heterogeneity of HIV among men who have sex with men (MSM) is necessary to inform HIV prevention and care strategies in the more generalised HIV epidemics across sub-Saharan Africa, including Malawi. We aimed to measure the HIV prevalence, risks, and access to HIV care among MSM across multiple localities to better inform HIV programming for MSM in Malawi.
Methods: Between Aug 1, 2011, and Sept 13, 2014, we recruited MSM into cross-sectional research via respondent-driven sampling (RDS) in seven districts of Malawi. RDS and site weights were used to estimate national HIV prevalence and engagement in care and in multilevel regression models to identify correlates of prevalent HIV infection. The comparative prevalence ratio of HIV among MSM relative to adult men was calculated by use of direct age-stratification.
Interpretation: HIV disproportionately affects MSM in Malawi with disparities sustained across the HIV care continuum. These issues are geographically heterogeneous and begin among young MSM, supporting geographically focused and age-specific approaches to confidential HIV testing with linkage to HIV services.