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Background:  Whether hepatitis C virus (HCV) is transmitted by unprotected sexual contacts is controversial.

Methods:  In the Swiss HIV Cohort Study (SHCS), HCV serotesting is done every 2 years and data about unsafe sex and injection drug use are gathered every 6 months. We assessed the incidence of HCV infection in the SHCS after April 2000 when a more detailed questionnaire about unsafe sexual behaviour was introduced. In patients with a heterosexual or men who have sex with men (MSM) transmission mode of HIV who denied injection drug use the association of HCV seroconversion and gender, age, and constancy of condom use was evaluated.

Results:  At entry, 1347 participants with heterosexual and 1542 with MSM HIV-transmission mode were HCV^–, did not report injection drug use and had a follow-up in the period of interest. Unsafe sex was reported by 28% of MSM, 34% of female heterosexual, and 25% of male heterosexual participants. Younger MSM participants tended to report more unsafe sex in (p < 0.001 for trend). There were 14 HCV seroconversions in MSM and 8 in heterosexual participants. In heterosexual the incidence rate was 0.2/100 person-years without a statistically significant association of unsafe sex or gender. In MSM who reported unsafe sex the incidence rate was 0.7/100 person-years, compared with 0.2/100 person-years in those not reporting unsafe sex (p = 0.02), corresponding to an incidence rate ratio of 3.5 (95% CI 1.2 to 10.0) (Figure 1). The hazard of acquiring HCV infection was increased among younger MSM participants (Figure 2). In a Poisson model including age, unsafe sex remained associated with acquisition of HCV with an IRR of 3.0 (95% CI 1.1 to 8.8, p = 0.04) in MSM.

Figure 1

Figure 2

Conclusions:  The incidence of HCV infection in HIV-infected persons is low in the absence of injection drug use. However, in HIV-infected MSM, unsafe sex is associated with an increased incidence of HCV infection.

Keywords: Hepatitis C Virus; transmission; unsafe sex