Detection of tenofovir in plasma samples , compared with no detection and as measured in seroconverters and a subset of non-seroconverters , was associated with an @ % relative risk reduction in HIV-@ acquisition for the tenofovir disoproxil fumarate group ( HR @ , @ % CI @-@ ; p < @ ) and @ % for the emtricitabine plus tenofovir disoproxil fumarate group ( @ , @-@ ; p < @ ) .