The risk of transmitting hepatitis C virus (HCV) through monogamous sex is very low, according to a new study of long-term heterosexual couples, HIVandHepatitis reports. Researchers from the University of California at San Francisco published their findings in the journal Hepatology of their cross-sectional study of 500 people with hep C—referred to as the “index person”—and their long-term partners. Couples were excluded from the study if either partner was infected with HIV or hepatitis B, had received an organ transplant, was on antiviral therapy, or if both of them had a history if injection drug use.

The index partners were mostly Caucasian, with a median age of 49 and a median 15 years of sexual history with their partners. The researchers interviewed each partner separately about their lifetime risks for hepatitis C infection, the sexual practices the couple experienced, and any sharing of personal grooming items. The scientists tested both partners for HCV and also performed genetic analyses to determine if each partner’s virus was related to the other in the event that both of them were infected.

A total of 20 couples were both infected with hep C, for a prevalence of 4 percent, 9 of which had the same genotype or serotype of the virus. Only three couples, however, had highly related viral isolates, indicating that one partner had infected the other. Basing their calculations on 8,377 person-years of follow-up, the scientists deduced that the maximum likelihood of hep C transmission between couples per year was 0.07 percent, or about one for every 190,000 sexual contacts.

For the HIVandHepatitis report, click here.

For the study abstract, click here.