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 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
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
“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.”