Methods: We followed an open cohort of 171 people, 152 women and 19 men, who were not initially infected by either HIV or HCV, and whose steady heterosexual partner presented antibodies to both viruses (index case). Other risk exposures were excluded. Every 6 months clinical, epidemiological, and risk behaviour information was collected, and antibodies to both viruses were determined.
Results: During 529 person years of follow up more than 40 000 vaginal or anal penetrations were recorded. 74 partners (43.3%) had vaginal and/or anal intercourse without condoms with the index case; another 15.8%, who always used condoms, declared breaking or slipping episodes during intercourse; and another 22.2% had unprotected orogenital exposures. During the follow up, over 5800 unprotected vaginal and anal contacts with the index case were estimated, as well as more than 25 000 unprotected orogenital contacts. 31 women became pregnant (two were index cases), and seroconversion to HIV occurred for one woman (1.7 per 10 000 unprotected contacts; 95% CI, 0 to 9.5), but there was no seroconversion to HCV (95% CI, 0–6.3 per 10 000 unprotected contacts).
Conclusion: These results are consistent with a low or null transmissibility of HCV in heterosexual relations, even when the index case is HIV co-infected.