Rigorous procedures will be maintained throughout the study to ensure full confidentiality of information obtained from participants. Data protection and anonymization procedures will be implemented and computerized matching methods will be used to ensure that access to linked data will be strictly limited to the principal investigators only, with the single exception that appropriate medical staff will be given access to results of HIV-1 or STD tests where participants wish to be informed of their results or to be offered treatment. The procedures will be such that staff, study participants and other individuals are not able to deduce individual HIV-1, STD and sexual behaviour details by applying exclusion and inclusion criteria. Confidential voting methods will be employed in the collection of sexual behaviour information so as to avoid the need for participants to impart personal information to enumerators.