Population Council Research that makes a difference

Abstract

Using capture-recapture methods for enumerating vulnerable and hard-to-reach populations 
Presentation at the 2009 HIV/AIDS Implementers' Meeting, Windhoek, Namibia, 10-14 June
Geibel,Scott; Sanders,Eduard J.; Luchters,Stanley
Publication date: 2009


Background and implementation approach
HIV prevention and treatment programs are increasingly targeting most-at-risk populations (MARPs), including female sex workers (FSWs), intravenous drug users (IDUs), and men who have sex with men (MSM). The sexual and/or drug-using behaviors of these populations, however, are illegal in most developing countries and thus members of these groups can be difficult to reach using traditional outreach methods. Additionally, these populations are generally highly stigmatized, making it difficult to efficiently identify, define, and allocate HIV resources for these hard-to-reach populations.

Analysis design and methods
In response to anecdotal evidence that a large number of MSM who sell sex were active in Mombasa, Kenya, we implemented a collaborative effort with local partners to enumerate male sex workers working in specific areas of Mombasa, using a capture-recapture methodology. Venues were identified where male sex workers seek clients, and MSM peers were recruited to identify and enumerate male sex workers. Records were kept of the location and time of each contact and of refusals to participate. The enumerations were conducted on two consecutive Saturdays. The final population estimate was derived using a capture-recapture calculation.

Results
The final population estimate was 739 (95% confidence interval, 690-798) male sex workers who sell sex in the study area. We found the capture-recapture exercise to be a relatively quick (approximately ten full training days, two full enumeration days) and inexpensive (approximately $10,000 of direct operational costs) way of enumerating male sex workers within a defined area (e.g., in or around a central business district). These enumeration results directly informed and improved the efficiency of both research and HIV prevention program activities.

Conclusions and recommendations
In 2009, the Population Council and partners are implementing further capture-recapture enumerations of MSM in South Africa and Nigeria. This activity is recommended for enumeration of other MARPs, including IDUs and FSWs, and is an efficient and low-cost strategy to determine size and distribution of MARPs in defined areas. Obtained results are valuable to inform programs and to better allocate HIV prevention resources.