Novel Approaches for Estimating Female Sex Worker Population Size in Conflict-Affected South Sudan

Abstract

Background Limited data exist describing the population size of female sex workers (FSW) in South Sudan. A population size estimation exercise among FSW was undertaken in Juba and Nimule during the Eagle Survey. Objective The study aimed to estimate the number of FSW in Juba and Nimule to inform resource allocation and service provision for FSW. Methods We utilized service and unique object multipliers, and 3-source capture-recapture methods in conjunction with a respondent-driven sampling (RDS) survey to estimate the number of FSW in Juba and Nimule. For service multiplier, the number of FSW testing for HIV in 2015 (Juba) and 2016 (Nimule) was obtained from the LINKAGES program targeting FSW. Survey participants were asked whether they had been tested for HIV by LINKAGES during the relevant period. A total of 2 separate unique object distributions were conducted in Juba and Nimule. In Nimule, these were combined to produce a 3-source capture-recapture estimate. The exercise involved distribution of key chains and bangles to FSW, documentation of the number of those who received unique objects, and questions during RDS survey to assess whether participants received unique objects. Results In Juba, the service multiplier method yielded an estimate of 5800 (95% CI 4927-6673) FSW. The unique object estimate (key chain and RDS participation) yielded 5306 (95% CI 4673-5939). Another estimate using RDS participation and receipt of a bangle yielded a much lower estimate of 1863 (95% CI 1776-1951), as did a 2-source estimate of key chain and bangle (2120, 95% CI 2028-2211). A 3-source capture-recapture estimate could not be produced because aggregate rather than individual level data were collected during the third capture. The multiplier estimate using key chain and RDS participation was taken as the final population estimate for FSW in Juba, which constitutes more than 6% of the female population aged 15 to 64 years. In Nimule, the service multiplier method yielded an estimate of 9384 (95% CI 8511-10,257). The 2-source estimates for key chain and RDS yielded 6973 (95% CI 4759-9186); bangles and RDS yielded a higher estimate of 13,104 (95% CI 7101-19,106); key chains and bangles yielded a lower estimate of 1322 (95% CI 1223-1420). The 3-source capture-recapture method using Bayesian nonparametric latent-class model-based estimate yielded a population of 2694 (95% CI 1689-6945), and this was selected as the final estimate for Nimule, which constitutes nearly 40% of female population aged 15 to 64 years. Conclusions The service and unique object multiplier, and 3-source capture-recapture methods were successfully used to estimate the number of FSW in Nimule, whereas service and unique object multiplier methods were successfully used in Juba. These methods yielded higher than previously estimated FSW population sizes. These estimates will inform resource allocation and advocacy e...

Population Size Estimation of Female Sex Workers in Hai Phong, Vietnam: Use of Three Source Capture–Recapture Method

“…By using Bayesian methodology, independence between capture histories can be accounted for. This methodology has been successfully implemented to estimate the PSE of KP in other countries such as Uganda [ 11 ] and South Sudan [ 12 ].…”

Evolving HIV epidemics

“…Multiplier methods can underestimate numbers if key population program data are limited or populations are unrecognized and/or inaccessible to surveyors, for example, when stigmatized population members misreport their risk. These issues have been observed in size estimation estimates in the region for both MSM and sex workers [49,50]. Serious efforts to improve size estimates have often used multiple methods [51–53] or applied innovative approaches, for example, Bayesian techniques applied to RDS multipliers [54] or combining venue-based sampling and RDS [55].…”

High HIV and syphilis prevalence among female sex workers in Juba, South Sudan

“…Mapping exercises of female sex workers (FSW) in 2010 and 2012 conservatively estimated between 2,000 and 2,500 FSW in Juba, respectively [ 4 , 5 ]. By 2015–2016, more robust methods produced an estimate of 5,800 FSW in Juba [ 6 ]. Sex work is illegal in South Sudan.…”