Prevalence of HCV and lack of evidence for sexual transmission among non-HIV-diagnosed MSM
In a sample of 821 non-HIV-diagnosed MSM recruited at a gay health centre in Zurich (Switzerland), we found an anti-HCV prevalence of 0.37% (0.12-1.69%); and a prevalence of active (acute or chronic) HCV infection of 0.12% (0.02-0.69%). To our knowledge, this is the first study to look at the prevalence of hepatitis C among non-HIV-diagnosed MSM in Switzerland. Although the level of reported sexually risky behaviours (UAI with different types of partners, numbers of sexual partners) and related indicators such as lifetime history of gonorrhoea and syphilis was substantial and comparable with other surveys on MSM in Switzerland , we found no evidence for elevated rates of sexual transmission of HCV in this population. Instead, being tattooed was marginally associated with a positive HCV serostatus, even when controlling for potential confounding factors. However, questions have been raised as to whether such associations might be due to residual confounding, as for low HCV-endemic countries such as Switzerland strict hygiene guidelines for tattoo and piercing studios have been implemented .
Overall, our results correspond well with previously published prevalence estimates from Sydney (Health in Men study), where 7 out of 824 HIV-negative men aged 18-75 years (0.85%) tested positive for HCV antibodies . As in the Australian study, we found no associations between HCV seropositivity and sexual practices that could have plausibly facilitated blood exposure, such as UAI and fisting. However, in a later longitudinal analysis, the Australian researchers found five HIV-negative men who seroconverted to HCV positivity (incidence of 0.11 per 100 person-years). Only one seroconverter reported IDU, four reported sexual contact with HIV-positive men, and two had an incident ulcerative sexually transmitted infection .
In the Montreal-based Omega cohort study of HIV-negative MSM, despite an anti-HCV baseline prevalence of 2.9%, only 1 seroconversion was identified (incidence of 0.038 per 100 person-years), and this infection could be attributed to IDU. The authors concluded that sexual transmission of HCV among non-HIV-diagnosed MSM appeared to be rare in 2001 . Based on 1,699 non-IDU MSM recruited in public health clinics in Seattle, San Diego, and New York City, a low (1.5%) prevalence of anti-HCV did not “support routine HCV testing of all MSM” .
In a recent study conducted in London, the anti-HCV prevalence among 965 HIV-negative men was 1.2% (0.6-2.1%) and thus “higher, but not significantly higher, than that in the general population (0.67%)” . Although the prevalence estimate among HIV-negative men in London was three times higher than in our Zurich sample, the authors recommend selective, not routine, HCV-testing among MSM according to the individual risk profile.
A recently published systematic review of studies on HCV-incidence among MSM concluded that the pooled incidence measure for HIV-negative MSM “is low and approximates that seen in the heterosexual population, where screening is not recommended” . The authors further suggest validating “the use of factors, such as at-risk sexual behaviour and the serology of sexual partners which are not always considered in medical assessments for targeting routine HCV-screening in HIV-negative MSM populations”.
In the Australian Trial in Acute Hepatitis C (ATAHC), sexual transmission among HIV-uninfected individuals “was unusual but was almost always in the context of contact with a known HCV-infected partner” .
Multiple studies have investigated the associations between HCV and UAI to identify possible routes of HCV transmission, producing divergent results. Although significant associations between UAI and HCV infection in MSM have been reported, the validity of some of these studies  is limited by a lack of adjustment for confounding behavioural factors. A recent prospective longitudinal cohort study  found a significant association between UAI and HCV infection, but did not include potential confounders that could explain other sexual or non-sexual routes of HCV infection, such as frequency of anal intercourse, group sex, sex-associated bleeding, traumatising sexual practices such as fisting, use of PDE-inhibitors, lesion-prone STIs (i.e. sexual), or (procto-)surgical interventions , tattooing or NIDU (i.e. non-sexual).
We were not able to replicate the commonly reported association between IDU and HCV infection, as none of the 22 MSM in our sample reporting IDU tested positive for HCV antibodies. Given the low number and proportion (3.3%) of MSM with IDU in the analytic sample, our study was not sufficiently powered to detect IDU as a risk factor for hepatitis C. However, the prevalences we found for current IDU, 3.1% among non-HIV-diagnosed MSM (95%-CI: 2.0-4.7), and 13.3% among HIV-diagnosed MSM (3.7-37.9%), are very similar to results from the largest Swiss MSM sample , where the respective values (IDU in the last 12 months among MSM in Zurich) were 3.7% and 17.0%.
Existing epidemiological studies on the association between non-injection drug use (NIDU) and HCV produced fairly consistent findings, indicating elevated HCV prevalence (2.3%-17%) in different NIDU samples. However, it still remains unclear whether HCV in people with NIDU can be attributed to undisclosed IDU or other residual confounding [49–51], although the biologic plausibility of intranasal transmission has been demonstrated [52–55]. In our sample NIDU of cocaine/amphetamines had substantial interaction with known HIV infection; and although none of the HCV-infected MSM without HIV diagnosis reported NIDU of snorting drugs, we cannot rule out that this behaviour constitutes an independent risk factor for HCV infection. Again, these findings highlight the need for further research in this area with more rigorous methodology needed to disentangle the specific pathways and risk factors for transmission.
With respect to HCV transmission among MSM–sexual or non-sexual–little attention has been given to the influence of social and sexual networks [56–58]. Particularly for gay men living with HIV, such networking has been described as serosorting, a practice sometimes conceptualised as a strategy to reduce HIV transmission risk. However, a more important motive for HIV-positive MSM to establish sexual contacts preferably with HIV-seroconcordant partners is to reduce stigma and sexual rejection . This consequently leads to a higher chance of exposure to STIs [60, 61]. With respect to hepatitis C it has further been hypothesised that “assortative mixing, or partnership formation within subgroups, is common and that this mixing pattern might result in HCV being more prevalent” . We hypothesize that sexual and social networks of MSM are the key to understanding the dynamics of sexual as well as non-sexual transmission of HCV. Taking into account networks and sub-group formation would in our view help to explain why HCV among HIV-positive MSM has spread so rapidly in the last decade . This would also explain why the HCV epidemic among HIV-positive MSM has not jumped to MSM without HIV diagnosis, despite individual behaviour that would facilitate HCV transmission in other sub-populations or networks.
Several study limitations need to be considered: First, the cross-sectional study design precludes the calculation of incidence rates and the investigation of causation, as it is uncertain whether reported behaviour preceded HCV infection or not. Second, as information on HIV diagnosis was based on self-report, the true HIV prevalence among participants is likely to be underestimated. Unfortunately, as anonymous testing was part of our study design, the serological test results could not be added post-hoc. However, focusing on MSM without serologically confirmed HIV serostatus reflects much better the situation of health care providers and counsellors when deciding whom to offer HCV-screening in a clinical setting. Third, the study has two important selection biases: MSM recruited predominantly at a gay health centre with a focus on STI services, or at sexual venues, respectively, are likely to over-represent individuals at higher risk for acquiring STIs. However, because HCV-testing was primarily offered to MSM anonymously testing for HIV and/or syphilis, both HIV-positive MSM as well as those with past Syphilis infection are likely to be under-represented in the sample. Also, HIV-diagnosed MSM with known active or past HCV-co-infection were not included in our sample. Fourth, given the overall anti-HCV prevalence of 0.83% in our sample, this study is not sufficiently powered to rule out an odds ratio of less than 6.0 for the association between any potential risk factor and HCV seropositivity. However, our results on HCV prevalence among non-HIV-diagnosed MSM can probably be generalised to community-based samples of MSM in Switzerland. Finally, some distortions due to missing data and misclassifications cannot be excluded. In systematically screened MSM, urethral, pharyngeal, and rectal manifestations of gonorrhoea are about equally frequent [63, 64], reflecting sexual practices of men who have sex with men. In contrast, in our sample, self-reported urethral gonorrhoea (19.6%) was more than ten times more common than pharyngeal (1.6%) or particularly rectal gonorrhoea (1.6%). This large discrepancy points towards a substantial under-diagnosis of rectal infections such as with Gonococci and Chlamydia, as suggested elsewhere . We therefore believe that the real lifetime history of “lesion-prone STIs” is substantially higher than suggested by our proxy measure.