Most of this risk came from receptive anal intercourse without a condom with partners with unknown serostatus ( PAF 53 % , prevalence 54 % , AHR 476 , 95 % CI 144-1571 ) ; by contrast , the PAF for receptive anal intercourse without a condom with an HIV-positive partner was 1 % ( prevalence 1 % , AHR 711 , 95 % CI 070-7275 ) .