Article Text

Download PDFPDF
How many men who have sex with men and female sex workers live in El Salvador? Using respondent-driven sampling and capture–recapture to estimate population sizes
  1. G Paz-Bailey1,2,3,
  2. J O Jacobson4,
  3. M E Guardado2,
  4. F M Hernandez2,
  5. A I Nieto5,
  6. M Estrada6,
  7. J Creswell7
  1. 1Del Valle University of Guatemala, Guatemala City, Guatemala
  2. 2Tephinet Inc., Atlanta, Georgia, USA
  3. 3University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
  4. 4Pan American Health Organization, Andean Region, Bogota, Colombia
  5. 5Ministry of Health, San Salvador, El Salvador, Colombia
  6. 6United States Agency for International Development, San Salvador, El Salvador, Colombia
  7. 7World Health Organization, Geneva, Switzerland
  1. Correspondence to Dr Gabriela Paz-Bailey, Del Valle University of Guatemala, 18 avenida 11-42 zona 15, Vista Hermosa III, Guatemala City 01015, Guatemala; gpaz{at}


Objective To estimate the numbers of female sex workers (FSW) and men who have sex with men (MSM) in San Salvador, El Salvador.

Design and methods A capture–recapture exercise was conducted among MSM and FSW in San Salvador in 2008. The first capture was done by distributing key chains to both MSM and FSW populations through local non-governmental organizations (NGO) that work with these groups. The second capture was done during the course of an integrated behavioural and biological survey (IBBS) using respondent-driven sampling (RDS). The proportion receiving a key chain estimated from the IBBS study was adjusted by RDS-derived weights.

Results The first capture included 400 FSW and 400 MSM. Of the 624 MSM interviewed in the IBBS, 36 (5.8% crude; 3.2% adjusted RDS) had received the key chain. The estimated population size of MSM in San Salvador was 12 480 (95% CI 7235 to 17 725). Of the 663 FSW interviewed in the IBBS, 39 (5.9% crude; 6.9% adjusted RDS) had received the key chain. The estimated number of FSW was 5765 (95% CI 4253 to 7277).

Conclusions The capture–recapture exercise was successfully linked to an IBBS to obtain city-level population sizes for MSM and FSW, providing valuable information at a low cost. Size estimates are crucial for programme planning for national AIDS programmes, NGOs and stakeholders working with these populations and for HIV projection models.

  • El Salvador
  • developing world
  • epidemiology
  • HIV
  • homosexual
  • MSM
  • population size estimates
  • RDS
  • respondent driven sampling
  • sex workers
  • sexual behaviour

Statistics from


  • Linked article 049171.

  • Portions of this study were presented at ISSTDR, London, 28 June–1 July 2009 2007 and the International AIDS Conference, Vienna, 18–23 July 2010.

  • Funding Funding for this study was provided by the United States Agency for International Development (USAID) in El Salvador and the Centers for Disease Control and Prevention (CDC).

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval This study was conducted with the approval of the ethical review board of the Rosales National Hospital (RNH) in San Salvador. The study was also reviewed by the Centers for Disease Control and Prevention–Global AIDS Program Associate Director for Science, who delegated approval to RNH.

  • Provenance and peer review Not commissioned; externally peer reviewed.

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

Linked Articles