Condomless sex sufficient to pass on hepatitis C between men

Image: Domizia Salusest |

Hepatitis C transmission during anal sex can take place without bleeding, trauma or sharing of injecting equipment and exposure to semen is likely to be enough for the virus to be passed on, investigators in the United States report in the journal PLOS ONE.

The conclusions come from an intensive investigation of ten cases of recent hepatitis C infection in eight gay men living with HIV.

The study was designed to investigate whether blood exposure is necessary for hepatitis C transmission during anal intercourse or if the virus can be passed on through condomless anal intercourse without bleeding. Previous studies have come to differing conclusions on this question; although hepatitis C virus can be found in semen and rectal fluid, several studies have concluded that condomless anal intercourse is not a risk factor for hepatitis C acquisition.



Having sex without condoms, which used to be called ‘unprotected’ or ‘unsafe’ sex. However, it is now recognised that PrEP and U=U are effective HIV prevention tools, without condoms being required. Nonethless, PrEP and U=U do not protect against other STIs. 


The last part of the large intestine just above the anus.

acute infection

The very first few weeks of infection, until the body has created antibodies against the infection. During acute HIV infection, HIV is highly infectious because the virus is multiplying at a very rapid rate. The symptoms of acute HIV infection can include fever, rash, chills, headache, fatigue, nausea, diarrhoea, sore throat, night sweats, appetite loss, mouth ulcers, swollen lymph nodes, muscle and joint aches – all of them symptoms of an acute inflammation (immune reaction).


The complete set of genes or genetic material (information) present in a cell or organism.


Moist layer of tissue lining the body’s openings, including the genital/urinary and anal tracts, the gut and the respiratory tract.

Instead, epidemiological studies which did not look at virus samples have identified factors such as fisting, anal trauma, bleeding and sharing of injecting equipment to inject methamphetamine as significant risks.

The new study led by Dr Hui Li of Perelman School of Medicine, University of Pennsylvania, used single genome sequencing and interviews with each of the men to establish the potential source of infection, asking them to recall their sexual and drug-using practices in recent sexual encounters.

Single genome sequencing takes a single virus and analyses its entire DNA sequence. This technique has been used in HIV research to demonstrate that the genetic diversity of infecting viruses increases when there is more damage to the mucosal barrier in the vagina or rectum.

In this study, the investigators hypothesised that if men infected with hepatitis C had only one virus genetic pattern detectable in multiple viruses sampled soon after infection, this showed a lack of damage to the mucosal barrier in the rectum.

In turn, this would signal a lower likelihood that rectal bleeding was necessary for transmission to take place. A lack of viral diversity would also show a lack of transmission through injecting drug use (where many genetically diverse viruses are transmitted).

"Hepatitis C prevention messages for gay men should clarify the potential for transmission during condomless anal intercourse."

They enrolled eight men with HIV who had acute or recent hepatitis C infection over a three-and-a-half-year period. Five were diagnosed with hepatitis C due to liver enzyme elevations and three by hepatitis C RNA testing.

All reported anal intercourse in the three months prior to diagnosis. Seven out of eight reported condomless receptive anal intercourse; in six of seven cases they recalled semen in the rectum. One of those also reported sharing injecting equipment to inject methamphetamine. One man reported insertive anal intercourse only. None reported anal trauma or bleeding.

A total of ten hepatitis infections were detected in the eight men. In one case, superinfection – acquisition of a second infection before the first had been cleared – was detected, while in the other case superinfection occurred during interferon treatment for an acute infection, diagnosed after viral load increase was detected during treatment.

Single genome sequencing was carried out on five samples from each man. Four patterns were evident.

  • In four infections, very low viral diversity was found, leading the investigators to conclude that each person was infected by one virus.
  • In a further four cases, genetic diversity was low enough that the investigators concluded that these infections also originated from one virus in each case.
  • In one case, viral diversity was greater, but still suggestive of a single-virus origin. Delay in sampling or infection with multiple viruses from someone themselves recently infected with a single virus were the most likely explanations for this pattern of diversity, the investigators concluded. This virus was isolated from a man who reported condomless anal intercourse without bleeding and no injecting.
  • Only one case exhibited a highly diverse virus population. This man reported condomless receptive anal intercourse with semen exposure and sharing of injecting equipment to inject methamphetamine during sex.

The researchers conclude that eight out of ten infections were attributable to a single virus, occurred without rectal trauma and were not associated with injecting. Sex does not need to be “traumatic”, cause bleeding or involve injecting to pose a risk of hepatitis C transmission, as hepatitis C virus is present in semen and rectal fluids. Injecting methamphetamine during chemsex probably poses less of a risk than heroin injecting because it doesn't require cooking or filtering, so there is less potential for blood contamination of injecting equipment, the study authors say.

Hepatitis C prevention messages for gay men should clarify the potential for transmission during condomless anal intercourse, they say. “Intra-rectal exposure to semen during condomless anal intercourse is therefore likely sufficient for hepatitis C virus transmission among men who have sex with men,” they conclude.


Li H et al. Assessing routes of hepatitis C transmission in HIV-infected men who have sex with men using single genome sequencing. PLOS ONE, 15: 0235237, 2020.