  Certain subpopulations like female sex workers (FSW), men who have sex with
men (MSM), and people who inject drugs (PWID) often have higher prevalence of
HIV/AIDS and are difficult to map directly due to stigma, discrimination, and
criminalization. Fine-scale mapping of those populations contributes to the
progress towards reducing the inequalities and ending the AIDS epidemic. In
2016 and 2017, the PLACE surveys were conducted at 3,290 venues in 20 out of
the total 28 districts in Malawi to estimate the FSW sizes. These venues
represent a presence-only data set where, instead of knowing both where people
live and do not live (presence-absence data), only information about visited
locations is available. In this study, we develop a Bayesian model for
presence-only data and utilize the PLACE data to estimate the FSW size and
uncertainty interval at a $1.5 \times 1.5$-km resolution for all of Malawi. The
estimates can also be aggregated to any desirable level (city/district/region)
for implementing targeted HIV prevention and treatment programs in FSW
communities, which have been successful in lowering the incidence of HIV and
other sexually transmitted infections.
