Participants ( n = @ ) were tested and treated for STIs ( chlamydia , gonorrhoea , syphilis and HIV ) and viral hepatitis ( hepatitis B and C ) , received HIV and STI prevention education and were randomized into four groups : ( @ ) control , ( @ ) medium conditional incentive ( $ @/six months ) , ( @ ) high conditional incentive ( $ @/six months ) and ( @ ) unconditional incentive ( $ @/six months ) .