- at low risk of HIV and willing to remain so for the duration of the study low risk of HIV infection defined as: no history of injecting drug use in the previous ten years no gonorrhoea or syphilis in the last six months no high risk partner (e.g. injecting drug use, HIV positive partner) either currently or within the past six months no unprotected anal intercourse in the last six months no unprotected vaginal intercourse outside a relationship with a regular known/presumed HIV negative partner in the last six months