Editor's Note: This article was first e-published March 25, 2005, on www.aidsmap.com.
Sexual transmission of hepatitis C virus (HCV) between HIV-negative gay men is extremely rare, according to a Canadian study published in the March 2005 edition of the American Journal of Public Health. In an eight-month period, only one incidence of HCV seroconversion occurred in a cohort of more than 1,000 gay men, and this case involved an individual who reported sharing injecting equipment in the previous six months.
There is considerable debate about the frequency of sexual HCV transmission, with epidemiological studies providing conflicting data. Studies in gay men have found a prevalence of HCV antibodies ranging from 1 percent in Denmark to 7 percent in Italy. Recent studies have suggested an increased prevalence and incidence of HCV coinfection in HIV-positive gay men, and it has been suggested that unprotected anal sex and fisting may be sexual activities which involve a significant risk of HCV transmission in this population.
In light of the conflicting data, investigators in Montreal examined the sexual transmission of HCV in a cohort of 1,054 gay men. This is the largest cohort of gay men in which the sexual transmission of HCV has been examined. These men were enrolled in the Omega Cohort Study, an ongoing prospective cohort into the risk factors of HIV transmission among gay men in Montreal. Enrollment started in 1996 and its objectives are to characterize changes in gay men's sexual behavior and to identify the psychological factors associated with sexual risk taking.
Men enrolled in the study provided a blood sample on entry to the study and then at intervals of six months. Between January 2001 and September 2001, 1,085 men provided consent to enter a substudy, and for their blood samples to be tested for HCV antibodies. If the result was positive, and the sample obtained on entry to the substudy was also positive, the individual was excluded from the incident study. However, if the baseline sample was HCV antibody negative, all serum samples obtained since the individual enrolled in the Omega Study were tested to determine the probable date of HCV seroconversion. All men completed a detailed questionnaire enquiring about sexual activity and possible routes of HCV transmission.
Median age was 32 years, and the men in the study had extensive sexual experience. In total, 92 percent of men reported anal sex at some time with either a regular or casual partner, and 63 percent of men said that they had had unprotected anal sex with either a regular or casual partner. More than 40 percent of men said that they had had 50 or more sexual partners in their lifetime, and 37 percent said that they had had unprotected anal sex with a casual partner. In addition, 44 percent of men said that they had had five or more regular partners in their lifetime and 56 percent said that they had had unprotected anal sex with a regular partner.
Of the 1,085 men who participated in the study, 32 were HCV-positive (3 percent). Of these, it was found that 31 were already infected at baseline. The remaining individual seroconverted between the first and second follow-up visits. When the investigators looked at the HCV-risk activities of the 31 men who had antibodies to the virus at baseline, they found that 20 were current injecting drug users (IDUs), eight were former IDUs, and three had no reported history of injecting drug use. Therefore, HCV prevalence among the 980 gay men in the study with no reported history of injecting drug use was 0.3 percent.
Hepatitis C virus prevalence was much higher among current IDUs (48 percent) than former IDUs (20 percent, P = 0.006), and unsurprisingly was also higher among drug users who reported sharing needles than those who had never shared needles (48 percent versus 13 percent, P = 0.002).
After controlling for injecting drug use, sexual behavior was not significantly associated with prevalent HCV infection. The investigators examined in more detail the sexual behavior of the three non-IDUs with HCV. They found that their sexual behavior did not differ significantly from HCV-negative men. Indeed, two of the three men said that they had used condoms 100 percent of the time. One man said he had had a blood transfusion and a body piercing, and the other two reported cocaine snorting and body piercing.
According to the investigators, "the 1,085 men who were [HCV]-negative at baseline contributed a total of 2,653 person-years of follow-up. With only one seroconversion, the overall incidence of [HCV] seroconversion was 0.038 per 100 person years."
Regarding this single seroconversion, the investigators note, "this seroconversion occurred in an [IDU] who reported needle sharing during the six months preceding the visit at which he first tested positive for [HCV]."