One-third of HIV-positive men who have sex with men (MSM) with recent or chronic hepatitis C (HCV) infection had detectable HCV in semen samples, researchers found in a 33-man study in New York City. The researchers calculate that HCV semen loads were high enough to transmit HCV during anal sex without a condom, according to the study.
An HCV epidemic has swept through populations of HIV-positive MSM in the United States and Western Europe. Research implicates receptive anal sex without a condom as the route of HCV transmission in MSM. But controversy surrounds the precise mechanism. Some attribute HCV transmission to rough, bloody anal sex, while others believe semen can transmit HCV without substantial anal trauma.
To address these issues, researchers analyzed semen and blood samples from HIV-positive MSM with recent or chronic HCV infection. They defined recent HCV infection as seroconversion within the past year and chronic HCV infection as seroconversion more than one year ago. Participants were asked to give three paired semen and blood samples at two-week intervals.
Of the 33 participating men, 21 (64%) had recent HCV infection (including four men reinfected after sustained virologic response to anti-HCV therapy) and 12 had chronic HCV infection. Median age was 36 in the recent HCV group and 52 in the chronic group. Respective proportions of whites were 57% and 58%, Hispanics 24% and 25%, and blacks 19% and 17%. Men with recent HCV had HIV infection for a median of seven years, compared with 10 years in the chronic HCV group. Nineteen men (58%) reported sex as their HCV risk factor, while 14 reported both sex and injecting drugs. All men reported receptive anal intercourse without a condom.
Among 59 evaluable semen samples, 16 (27%) had detectable HCV. Eleven of the 33 participants (33%) had detectable HCV in their semen. Median HCV load in semen with detectable HCV was 1.49 log10 IU/mL (about 30 IU/mL). The researchers found a significant correlation between HCV load in blood and semen in the overall group (rs = 0.41, P = .001). The recent and chronic HCV groups did not differ significantly in proportion of semen specimens with detectable HCV (21% and 38%, P = .2) or in median HCV load in semen (1.32 versus 1.77 log10 IU/mL, P = .2).
Among 11 men with recent HCV infection who provided multiple semen samples, four (36%) had HCV detectable in at least one sample and one (9%) had HCV detectable in all semen samples. Among six men with chronic HCV who provided multiple semen samples, four (67%) had HCV detectable in at least one sample and three (50%) had HCV detectable in all samples.
On the basis of the HCV loads measured, the researchers calculate that an average ejaculate would deliver between 50 and 6630 IU of virus into the rectum. Because as few as 10 to 20 HCV particles transmitted parenterally can establish HCV infection, the authors believe the semen HCV loads they calculate can transmit HCV rectally without trauma to the rectum. "While more 'traumatic' acts such as fisting or even vigorous penile insertion may increase susceptibility to HCV," they suggest, "we have demonstrated that semen often contains HCV and postulate that this semen contains sufficient virus to transmit infection to anal-receptive partners."