Participants ( n = 267 ) 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 : ( 1 ) control , ( 2 ) medium conditional incentive ( $ 50/six months ) , ( 3 ) high conditional incentive ( $ 75/six months ) and ( 4 ) unconditional incentive ( $ 50/six months ) .