To determine operational and analytical characteristics of respondent-driven sampling (RDS) in international settings and to explore factors that may affect recruitment of most-at-risk populations using RDS, we reviewed HIV biological and behavioral surveillance studies that used this method outside of the United States. We identified 123 eligible studies, 59 from Europe, 40 from Asia and the Pacific, 14 from Latin America, seven from Africa and three from Oceania. Studies collectively recruited 32,298 participants between 2003 and 2007; 53% of studies were conducted among injecting drug users, which generally had faster recruitment compared with studies among sex workers. All but 13 studies reached > or = 90% of their intended sample size, and six studies failed to reach equilibrium for key variables. This review has shown that RDS is an effective technique, when designed and implemented appropriately, to sample most-at-risk populations for HIV biological and behavioral surveys.

Using respondent-driven sampling (RDS), we gathered data from 128 HIV surveillance studies conducted outside the United States through October 1, 2007. We examined predictors of poor study outcomes, reviewed operational, design and analytical challenges associated with conducting RDS in international settings and offer recommendations to improve HIV surveillance. We explored factors for poor study outcomes using differences in mean sample size ratios (recruited/calculated sample size) as the outcome variable. Ninety-two percent of studies reported both calculated and recruited sample sizes. Studies of injecting drug users had a higher sample size ratio compared with other risk groups. Study challenges included appropriately defining eligibility criteria, structuring social network size questions, selecting design effects and conducting statistical analysis. As RDS is increasingly used for HIV surveillance, it is important to learn from past practical, theoretical and analytical challenges to maximize the utility of this method.

Obtaining samples of populations at risk for HIV challenges surveillance, prevention planning, and evaluation. Methods used include snowball sampling, time location sampling (TLS), and respondent-driven sampling (RDS). Few studies have made side-by-side comparisons to assess their relative advantages. We compared snowball, TLS, and RDS surveys of men who have sex with men (MSM) in Forteleza, Brazil, with a focus on the socio-economic status (SES) and risk behaviors of the samples to each other, to known AIDS cases and to the general population. RDS produced a sample with wider inclusion of lower SES than snowball sampling or TLS-a finding of health significance given the majority of AIDS cases reported among MSM in the state were low SES. RDS also achieved the sample size faster and at lower cost. For reasons of inclusion and cost-efficiency, RDS is the sampling methodology of choice for HIV surveillance of MSM in Fortaleza.