The annual incidence of hepatitis C infection in gay men with HIV is now nearly twice that seen in HIV-positive injecting drug users, according to a Swiss study.
Hepatitis C infections started increasing substantially from 2005 onwards, the study finds, and there is an accelerating trend, with a particularly large increase in infections in the last year.
The Swiss HIV Cohort Study (SHCS) of the largest and most complete cohorts of HIV patients in the world; it includes the majority of HIV-positive people in Switzerland. Annual tests for hepatitis C became routine in 1998.
This survey looked at 6534 patients who were hepatitis C negative at the point they entered the SHCS and who have had at least one other hepatitis C test since then. In terms of the original route-of-exposure group they belonged to when diagnosed with HIV, 3333 patients (51%) were gay men, 3078 (47%) were heterosexual and 123 (2%) were injecting drug users. For the sake of clarity, patients who were both gay and IDU were excluded from the study, as were heterosexuals who started infecting drugs after HIV diagnosis.
Since 1998 there were 167 new cases of hepatitis C infection of which 101 (60%) were in gay men. But half of the cases in gay men happened since 2009; in the last three years 51 out of 65 new cases of hepatitis C (78%) were in gay men.
Incidence rates have changed dramatically since 1998. In that year the annual incidence of hepatitis C in HIV-positive injecting drug users was 13.9% and it fell to 2.2% a year in 2001. In contrast annual hep C incidence in gay men was just 0.2% a year in 1998 and is now 4.1%, an 18-fold increase.
There has also been a less dramatic increase in non-injecting heterosexuals: hepatitis C incidence was under 0.1% a year in 1998 and is now about 0.8%.
In multivariate analysis, three risk factors stood out in gay men, each roughly doubling the risk of hepatitis C infection: inconsistent condom use, a past history of syphilis, and being already infected with hepatitis B.
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