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Hepatitis C Levels in Rectal Fluid Explains Transmission to Insertive Sex Partners

January 24, 2017

Hepatitis C (HCV) in rectal fluid of HCV/HIV-infected men who have sex with men (MSM) reaches levels high enough to expose the penis of insertive sex partners to at least 2300 IU of HCV throughout anal intercourse -- enough to establish HCV infection. This single-center study detected HCV in rectal fluid of 20 of 43 men (47%).

An epidemic of sexually transmitted HCV among HIV-positive men has continued for a decade or more in Europe, the United States and other countries. Although studies identify condomless receptive anal intercourse as a risk factor for HCV acquisition, controversy surrounds the mechanism of this transmission. Some work implicates rectal bleeding, but other research implicates semen. How the insertive partner may become infected remains an open question.

To get a better understanding of HCV transmission in HIV-positive MSM, New York City researchers studied HIV-positive MSM in care for recent or chronic HCV infection. Health workers rotated polyester-tipped swabs in the anal canal of these men to collect fluid. They examined swabs for blood then assayed the fluid for HCV viral load. The first 30 men studied underwent high-resolution anoscopy after swabbing to look for blood and other abnormalities. Study participants gave blood samples on the same day as anal fluid sampling.

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The study included 45 MSM with a median age of 43 years (interquartile range [IQR] 33 to 49). While 60% of men were white, 18% were Hispanic and 16% black. Median HCV RNA in blood stood at 5.9 log10 IU/mL (IQR 3.9 to 6.5). Although 43 men (96%) were taking antiretroviral therapy, 22 (49%) had a detectable HIV load. High-resolution anoscopy performed on the first 30 men enrolled found no blood, swab-related injury or relevant pathology. Anoscopy performed on one man who enrolled later revealed blood, the only detection of visible blood in these 45 men.

Twenty of 43 men (47%) with evaluable rectal samples had HCV in rectal fluid at a median level of 2.9 log10 IU/mL (about 800 IU/mL). Based on median rectal fluid HCV level, the researchers calculated that the surface of an average penis would be exposed to at least 2300 IU of HCV throughout anal intercourse.

HCV blood level was significantly higher in men with than without rectal fluid HCV (6.4 versus 4.0 log10 IU/mL, P < .001). High proportions of men with HCV above 5 log10 IU/mL in blood (85%) and above 6 log10 IU/mL in blood (90%) had HCV detectable in rectal fluid. Those HCV loads in blood are in the typical range for HIV-infected men with untreated chronic HCV infection. Rectal HCV level correlated strongly with blood HCV (rs = 0.69, P < .001).

The researchers believe their findings provide "the first direct evidence that a sufficient quantity of HCV is shed into the rectum of HIV-infected men with HCV infection to directly infect an inserted penis" or for the insertive partner to pick up HCV and pass it to a subsequent anal sex partner. They suggest that the proportion of men with HCV in rectal fluid may be "much higher than half" since rectal fluid HCV correlated with HCV in blood, and most men in this study had early HCV infection with low blood loads.

Together with previous work demonstrating that HCV is shed in semen at levels high enough to transmit HCV during sex, the authors "believe that semen and rectal fluid, rather than frank blood from the rectum, are likely the fluids that mediate most HCV infections in this epidemic." The authors call for "an appropriate public health campaign to educate MSM about these routes of HCV infection to reverse the HCV epidemic among HIV-infected MSM."

Mark Mascolini writes about HIV infection.


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