Each partner independently reported time periods of sexual activity and the number of contacts per month during that time period. Since the time periods reported by each partner might not match perfectly, we calculated the number of contacts per time period per partner and summed the estimated number of contacts Vismodegib per each partner over the duration of the relationship. The average of the total number of contacts reported by partner 1 and partner 2 was used as the total number of contacts for the couple. Prevalence of anti-HCV positivity and 95% CIs were calculated for the partners

of index subjects. Incidence of sexually acquired HCV infection was estimated per number of sexual contacts (vaginal intercourse with and without menses and anal intercourse). Incidence density of HCV infection was calculated as the number of potential transmission events per total person-years of sexual relationship reported among partners. Duration of the sexual relationship was summed among the 500 partners to determine the total person-years of

observation. Of the 2,077 couples screened for study inclusion, 672 (32%) were eligible. Reasons for study exclusion occurring in ≥5% of the 1,405 ineligible couples included lack of sexual activity (31%), prior organ transplant (12%), refused study participation (11%), doctor refused (8%), HIV or HBV coinfection (8%), partnership less than 3 years or nonmonogamous (6%), and history of IDU in both partners (6%). Of the 672 eligible couples, 500 (74%) enrolled and completed all the study requirements, at which time study enrollment was halted. The primary reasons Selleckchem Stem Cell Compound Library for failure MCE to participate among the remaining 172 eligible couples were nonresponse (54%) or refusal (29%). Of the 500 enrolled couples, 43% were referred from tertiary referral practices, 34% from community sources, and 21% were blood donors. The 500 couples were predominantly non-Hispanic white, educated, employed, and born in the United

States (Table 1). The median duration of the couples’ sexual relationships was 15 years (range, 2-52 years). The most frequently reported risk factors for HCV infection among index subjects were IDU (53.8%) and blood transfusion before 1992 (31.6%); these risks were infrequently reported by partners. Twenty or more lifetime sex partners prior to the current relationship were reported by 46.2% of index subjects and 26.8% of partners. The median number of sexual contacts per month was highest for vaginal intercourse during the first year of the relationship (12 contacts per month) (Table 2). The frequency of sexual contacts decreased over time for all types of sexual activity. Vaginal intercourse during menses and anal intercourse (≥1 occasion) were reported by 65.2% and 30.4% of couples, respectively. Condom use during vaginal intercourse was reported by 29.9% of couples and condom use decreased over time for vaginal and anal intercourse.