Innovative approaches to cohort retention in a community-based HIV/STI prevention trial for socially marginalized Peruvian young adults.

Background: The conduct of longitudinal clinical trials must involve effective strategies to retain study participants in order to ensure internal validity, adequate statistical power and generalizability of results.

Purpose: In a large trial in Peru, we implemented various retention strategies to maintain high participation rates over time.

Methods: Novel participant retention strategies were used to follow highly marginalized populations for two years because traditional locator information, such as telephone numbers and official identification (eg, passport, driver's license, the local equivalent of a social security number) were often unreliable or unavailable.