Around one in five HIV-positive gay men who recently acquired hepatitis C report anal sex without a condom as the only behaviour that could explain their infection. At the same time, a third of people acquiring hepatitis C were gay men who did not have HIV, clinicians from the Mortimer Market Centre in London told the British HIV Association (BHIVA) conference in Liverpool last week.

The data suggest that prevention messages around sexually transmitted hepatitis C need to change.

Prevention advice has tended to focus on sexual practices which could result in trauma to the rectum (such as fisting and use of sex toys), sometimes with additional reference to behaviours commonly reported by gay men who acquire hepatitis C (such as group sex and chemsex).

However, several studies have identified receptive anal sex without condoms as a risk factor. In the last year, American researchers have demonstrated that hepatitis C virus can be found at infectious levels both in semen and the rectal mucosa. This fundamentally challenges the belief that hepatitis C can only be transmitted in blood.

Moreover, until now, most cases of sexually transmitted hepatitis C have been in gay men living with HIV, but clinicians have begun to identify cases of hepatitis C in HIV-negative gay men, especially among men using pre-exposure prophylaxis (PrEP).

It is possible that, previously, hepatitis C was concentrated in networks of HIV-positive men due to serosorting. Increasing knowledge of treatment as prevention and use of PrEP may now mean that more HIV-negative gay men are having condomless sex with HIV-positive men. While those HIV-negative men will be protected from HIV, they may be exposed to hepatitis C.

Clinicians at the Mortimer Market Centre in central London noticed that some of their patients diagnosed with acute (recently acquired) hepatitis C did not fit the expected profile. They therefore reviewed the case notes of the 48 patients diagnosed with acute hepatitis C at the clinic between April 2015 and April 2016.

Of the 48 cases, 81% were in gay and bisexual men, 6% were in heterosexual men and 13% were in women. Whereas 67% were in people living with HIV, 33% were in HIV-negative people.

Among the HIV-positive people who acquired hepatitis C, anal sex without a condom was commonly reported (75%). Many HIV-positive people reported recognised risk factors, including injecting drug use (31%), chemsex (drug use in a sexual context, 53%) and snorting drugs (53%). Only 3% reported fisting.

However, there were 19% of HIV-positive people with acute hepatitis C whose only risk factor was sex without a condom.

Significant numbers of HIV-positive people with acute hepatitis C had sexually transmitted infections (59%) including rectal infections (28%).

Risk factors for HIV-negative people were somewhat different. In particular, none of this group reported anal sex without a condom as their only risk factor (although 44% did report this behaviour alongside other risk factors).

Hepatitis C in HIV-negative people appeared to be driven by injecting drug use (44%), chemsex (38%) and snorting drugs (38%). Again, fisting was infrequently reported (6%).

One-quarter of HIV-negative people acquiring hepatitis C were using PrEP.

In contrast to those with HIV, sexually transmitted infections were quite rarely reported (6%).

The researchers recommend that HIV-negative gay men who can be identified as being at a higher risk of hepatitis C are offered testing for the virus. This would include PrEP users, men reporting chemsex or injecting drug use and the sexual partners of people with hepatitis C.

They also recommend that gay men living with HIV are advised that hepatitis C can be passed on through anal sex without a condom.