Of 52 incident HIV-1 infections , 31 occurred in individuals assigned tenofovir disoproxil fumarate ( incidence 071 cases per 100 person-years ) and 21 were in those assigned emtricitabine plus tenofovir disoproxil fumarate ( 048 cases per 100 person-years ) ; HIV-1 incidence in the placebo group until discontinuation was two cases per 100 person-years .