Almost half of MSM with HIV/HCV co-infection have HCV in their rectal fluid

Almost half of HIV-positive men who have sex with men (MSM) who have co-infection with hepatitis C virus (HCV) have detectable HCV in their rectal fluid, US investigators report in the online edition of Clinical Infectious Diseases. The presence and level of HCV in rectal fluid was strongly associated with the level of HCV in blood.

“This study provides the first direct evidence that HCV is shed into the rectum of HIV-infected men,” comment the authors. “We found HCV at substantial levels in the rectal fluid of almost half the HIV-infected men we studied.”

The authors believe their findings support the hypothesis that rectal bleeding is not needed for the sexual transmission of HCV infection between MSM. They call for the development of health promotion interventions that reflect their findings.

The first cases of sexual transmission of HCV involving HIV-positive MSM were reported in the early 2000s and there are now well-established epidemics of sexually transmitted HCV involving HIV-positive MSM in a number of European and US cities. Despite this, there is still considerable uncertainty about the body fluids involved in transmission and the precise sexual practices that carry the highest risk of infection with the virus.

Investigators in New York City therefore designed an observational study involving 43 HIV-positive MSM with HCV co-infection. HCV viral load was quantified in paired samples of rectal mucus and blood. Sixty per cent of participants were white and the median age was 43 years. All were taking antiretroviral therapy, but because of poor adherence, only 49% had viral suppression.

Two-thirds of participants had high-resolution anoscopy at the time rectal fluid was sampled. None of these individuals had evidence of rectal trauma or bleeding. However, blood was detected on the rectal swab from a man who did not initially undergo anoscopy. Subsequent anoscopy revealed the presence of proctitis.

HCV in rectal fluid was detected in 47% of men. The median HCV viral load in rectal fluid was 2.9 log₁₀ IU/ml. Blood viral load was significantly higher among men with HCV in their rectal fluid compared to those in whom it was not detected (6.4 log₁₀ IU/ml vs. 4.0 log₁₀ IU/ml, respectively, p < 0.001).

The presence of HCV in rectal fluid was strongly associated with HCV viral load in blood above 5 log₁₀ IU/ml (p = 0.001) and even more strongly with blood HCV viral load above 6 log₁₀ IU/ml (p < 0.001). Moreover, 85% of those with a blood HCV viral load above 5 log₁₀ IU/ml and 90% of individuals with a blood HCV viral load above 6 log₁₀ IU/ml had HCV in their rectal fluid.

There was a significant positive correlation between the level of HCV in rectal fluid and HCV viral load in blood. High-level rectal shedding of HCV – 4 to 5 log₁₀ IU/ml – was detected in a quarter of individuals with a blood viral load above 6 log₁₀ IU/ml. The man with the highest rectal HCV viral load (5.2 log₁₀ IU/ml) was the person with visible blood on his rectal swab and proctitis.

“These results support the accumulating epidemiological evidence that rectal bleeding is not required for transmission of HCV infection among HIV-infected MSM, and may be the explanation for the epidemiological associations found in some studies between group sex or fisting,” write the authors. “We suggest that for clinical and public health purposes, finding HCV RNA in rectal fluid should be taken as evidence of infectiousness until proven otherwise.”

The authors conclude that, “semen and rectal fluid, rather than frank blood from the rectum, are likely the fluids that mediate most HCV infections in this epidemic.” They call for public health campaigns to educate MSM about these routes of HCV transmission.