Reassessing geographic bottlenecks in a respondent-driven sampling based multicity study in Brazil

This study analyzes the spatial dynamics of drug users' recruitment chains in the context of a respondent-driven sampling (RDS) study in the city of Recife, Brazil. The purpose is to understand the geographic bottlenecks, influenced by social geography, which have been a major challenge for RDS-based studies. Temporo-spatial analysis was used. Sequential maps depicted the dynamics of the recruiting process, considering neighborhood of residence and/or places of drug use. Poisson regression was fitted to model the recruiting rate by neighborhood of residence and/or places of drug use, and the different neighborhoods' demographics. The distance between neighborhood of residence and/or places of drug use and the assessment center was negatively associated with recruitment. There was a positive association between the proportion of the population living in informal settings and the recruiting rate per neighborhood of residence and/or places of drug use. Recruitment chains depend on the social geography and demographics of the population. Studies should incorporate seeds from as many neighborhoods as possible, and more than one assessment center should be utilized.