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.
When somebody who already has a viral infection is exposed to a different strain or a different virus, and acquires it in addition to their existing virus. For example a person with hepatitis C is infected with a different strain of hepatitis C, or a person with chronic hepatitis B is infected with hepatitis D.
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
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
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
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).
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
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
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
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
- 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.