Unprotected sex is associated with new hepatitis C virus infections in Swiss HIV-positive gay men, according to a study published in the August 1st edition of Clinical Infectious Diseases. This finding supports other studies which have found evidence of the sexual transmission of hepatitis C virus between HIV-positive gay men.
Swiss investigators believe that their study has added weight to the earlier research, “being the first report of an association on unprotected sex with an increased incidence of hepatitis C virus infection in HIV-infected [gay] men that was determined on the basis of a prospective longitudinal cohort that included regular hepatitis C virus testing and reports about condom use and injecting drug use.”
Although it is well established that there is a high prevalence of hepatitis C virus infection amongst HIV-positive individuals, there is little information concerning the incidence of new hepatitis C infections in this population. The few studies that have investigated this have found a low incidence of new infections related to heterosexual intercourse, although genital ulceration is thought to facilitate heterosexual transmission.
Although there is little evidence of sexual transmission in HIV-negative gay men, data from studies conducted amongst HIV-positive gay men in London and some other western cities suggest increasing hepatitis C infection rates among HIV-positive men engaging in unprotected anal sex and harder sexual practices such as fisting.
In the Swiss HIV cohort, hepatitis C prevalence is measured and information regarding injecting drug use and condom use is collected every six months. Investigators were therefore able to study the incidence of hepatitis C virus infection related to sexual behaviour and drug use.
Since 1998 patients in the Swiss Cohort have been regularly tested for hepatitis C virus and frozen plasma samples from before this time have been retrospectively tested. Syphilis test results are also available for approximately two-thirds of patients.
Individuals complete questionnaires regarding their drug use and sexual behaviours on entry to the study and every six months thereafter.
Overall prevalence of hepatitis C virus infection was 33% amongst 7899 members of the cohort enrolled since 1988. Over 90% of these infections were in injecting drug users.
Hepatitis C virus incidence was calculated on data from 3327 individuals. A total of 104 new hepatitis C virus infections were detected in these patients in a total of just over 16,000 patient years of follow-up. This provided an incidence of 0.64 cases per 100 person years.
Incidence was highest amongst injecting drug users at 7.4 cases per 100 person years, compared to 0.23 cases per 100 person years amongst individuals with no history of injecting drugs.
Amongst gay men who had not injected drugs, but who had had unprotected anal sex had an incidence rate of 0.7 per 100 person years compared to 0.2 per 100 person years for gay men reporting neither injecting drug use nor unprotected sex. This difference was statistically significant (p = 0.02) and the incidence rate ratio was 3.5.
The investigators also found a trend for incident hepatitis C virus infections amongst younger gay men and a significant association between infection with syphilis and hepatitis C virus infection (p = 0.03).
No significant relationship was found between unprotected sex and infection with hepatitis C virus amongst heterosexuals in the cohort.
“Data of the large, prospective Swiss HIV Cohort Study indicate that unsafe sexual behaviour amongst [gay] men is associated with new acquisitions of hepatitis C virus infection”, conclude the investigators.
Rauch A et al. Unsafe sex and increased incidence of hepatitis C virus infection amongst HIV-infected men who have sex with men: the Swiss Cohort Study. Clin Infect Dis 41 (On-line edition), 2005.