Multicenter cohort study of individuals reporting behavioral risks of HIV acquisition, recruited among those presenting for testing for HIV and other sexually transmitted infections. Overarching goal: to study factors associated with uptake of HIV prevention and (re)testing services in medium-sized cities in Thailand. Primary objective: To estimate the incidence of HIV and other sexually transmitted infections (syphilis, chronic hepatitis B and C) among individuals presenting for retesting. Secondary objectives: * To evaluate the uptake of pre-exposure prophylaxis * To assess retention in the study * To evaluate client HIV knowledge * To describe HIV prevalence and characteristics of individuals newly diagnosed with HIV * To describe characteristics of individuals at risk of HIV infection * To assess the quality of the testing and referral services.