Sexual transmission of hepatitis C very rare in monogamous heterosexual couples

Sexual transmission of hepatitis C virus (HCV) among monogamous heterosexual couples is extremely rare, investigators from the United States report in Hepatology. The maximum incidence of sexual transmission was just 0.07% per year, equivalent to just one transmission per 190,000 sexual contacts. No specific sexual behaviours showed a significant association with sexual transmission of the virus.

The investigators believe “the extremely low estimated risk for HCV infection in sexual partners, [and] the lack of association with specific sexual practices provides unambiguous and reassuring counseling messages.”

Most HCV infections are the result of contact with infected blood, though the accumulated evidence suggests that sexual transmission is possible. However, HCV appears to be less likely to be sexually transmitted than either hepatitis B virus (HBV) or HIV.

Nevertheless, the frequency of sexual HCV transmission has been the subject of scientific controversy. As the authors note, “the lack of quantifiable data has been a limitation to clinicians counseling their patients”.

Investigators in California therefore designed a cross-sectional study involving 500 heterosexual, sexually active, monogamous couples where one partner was chronically infected with HCV. Their aims were to estimate the frequency of sexual transmission of HCV and to see if any sexual practices were associated with an increased risk.

Participants were recruited between 2000 and 2003. They were required to have been in a monogamous sexual relationship for at least three years and to be currently sexually active. The study was limited to heterosexual couples. Current injecting drug users as well as individuals with HBV or HIV co-infection were excluded, as were couples where the partner with HCV was taking antiviral drugs.

The patients with HCV and their partners had HCV antibody and viral load tests. The people with HCV also had genotype analysis. In circumstances where partners were found to have concordant genotype infection, phylogenetic analysis was performed to see if the infections were genetically linked, possibly indicating sexual transmission.

The patients and their partners were interviewed separately about their sexual behaviour. Participants were also questioned about their sharing of grooming and hygiene equipment, such as toothbrushes, nail clippers and razors.

The couples had been together for a median of 15 years and had a median age of 48 years. Approximately three-quarters were white.

The frequency of sexual activity declined with relationship duration. As HCV is primarily a bloodborne virus, participants were asked about sexual behaviour that potentially involved contact with blood. Vaginal intercourse during menses was reported by 65% of couples and 30% reported anal sex.

Approximately 17% of couples frequently used condoms during the first year of the relationship, frequent use falling to 13% in the year of the study. Frequent use of condoms for anal sex was rare and never above 13%.

In all, 20 partners of patients with HCV were found to have antibodies to the virus and 13 of these individuals had detectable HCV viral load. The HCV genotype was concordant in nine couples. Phylogenetic analysis was possible for six couples. This showed that the virus was closely linked between the partners in three couples.

The prevalence of HCV infection potentially attributable to sexual transmission ranged from a low of 0.6% (the three couples shown to have genetically linked infections) to a high of 1.2% when the three couples whose virus was not suitable for phylogenetic analysis were categorised as having linked infections.

The estimated incidence of sexual HCV transmission ranged from 3.6 per 100,000 person years, or one transmission per 380,000 sexual contacts, to a maximum of 7.2 per 100,000 person years, a transmission every 190,000 sexual acts.

“Sexual transmission of HCV among monogamous heterosexual couples is an extremely infrequent event,” comment the authors. “Condom use was infrequent among the study participants and decreased over the duration of the sexual relationship, indicating that the very low rate of sexual transmission in our study was not due to the use of barrier methods during sexual activity.”

The investigators were unable to pinpoint any sexual practices linked with an increased risk of sexual transmission. However, couples in which possible sexual transmission occurred were more likely to report vaginal sex during menses (100 vs 66%) and anal sex (67 vs 30%) than couples where there was no evidence of sexual transmission, and they also reported less frequent condom use (0 vs 30%). However, none of these differences were statistically significant.

“The very low estimated overall transmission rate indicates that that any risk from infection from engaging in specific high-risk practices would be very low,” write the authors.

They suggest that the outbreaks of sexually transmitted HCV recently reported in HIV-positive gay men in a number of countries are likely due to “disrupted mucosal integrity” and the effects of HIV co-infection.

“HCV transmission by sex from chronically infected persons to their heterosexual partners in a long-term relationship likely occurs, but is a rare event,” conclude the authors, who believe their findings support current recommendations “that couples not change their sexual practices if they are in a monogamous heterosexual relationship.”