JMIR Publications

ABSTRACT

Background:

Key populations at higher risk for HIV infection, including people who inject drugs (PWID), men who have sex with men (MSM), and female sex workers (FSW) are disproportionately affected by the HIV/AIDS epidemic. Empirical estimates of their population sizes are necessary for HIV program planning and monitoring. Such estimates however are lacking for most of Uganda’s urban centers.

Objective:

To estimate the number of female sex workers (FSW) and men who have sex with men (MSM) in select locations in Uganda.

Methods:

We utilized conventional 2-source capture-recapture to estimate the population of FSW in Mbale, Jinja, Wakiso, Mbarara, Gulu, Kabarole, Busia, Tororo, Masaka, and Kabale and of MSM in Mbale, Jinja, Wakiso, Mbarara, Gulu, Kabarole, and Mukono from June – August 2017. Hand mirrors and key chains were distributed to FSW and MSM, respectively, by peers during capture one. A week later, different FSW and MSM distributors went to the same towns to collect data for the second capture. Population size estimates and 95% confidence intervals (CI) were calculated using the capture-recapture Simple Interactive Statistical Analysis (SISA). Prediction surface maps were created using the Kriging interpolation method for MSM and FSW densities for each town in ArcMap 10.3.1.

Results:

We estimated the population of FSW and MSM using two different recapture definitions: those who could present the object and those who could present the object or identify the object from a set of photos. The most credible estimates came from those who presented the objects only. The FSW population in Mbale was estimated to be 693 (95% CI: 474-912). For Jinja, Mukono, Busia, and Tororo, we estimated the number of FSW to be 802 (95% CI: 534-1069), 322 (95% CI: 300-343), 961 (95% CI: 592-1330), and 2872 (95% CI: 0-6005). For Masaka, Mbarara, Kabale, and Wakiso, we estimated the FSW population to be 512 (95% CI: 384-639), 1904 (95% CI: 1058-2749), 377 95% CI: (247-506), and 828 (95% CI: 502-1152), respectively. For Kabarole and Gulu, we estimated the FSW population to be 397(95% CI: 325-469) and 1425 (95% CI: 893-1958). MSM estimates are 381(95% CI: 299-462) for Mbale, 1100 (95% CI: 351-1849) for Jinja, 368 (95% CI: 281-455) for Wakiso, 322 (95% CI: 253-390) for Mbarara, 180 (95% CI: 170-189), for Gulu, 335 (95% CI: 258-412) for Kabarole, and 264 (95% CI: 228-301) for Mukono.

Conclusions:

The capture-recapture activity was one of the first done in Uganda to obtain small town-level population sizes for FSW and MSM. The prediction maps of MSM and FSW densities provide useful information for HIV program planning. We found that it is feasible to use FSW and MSM peers for this activity, but proper training and standardized data collection tools are essential to minimize bias.