The other is that these are baseline figures, so tell us nothing about the impact of PrEP itself. What do we know about HIV incidence, as opposed to prevalence, in HIV-positive and negative gay men?
In HIV-positive men, the HCV infection rate has been rising. In the CASCADE cohort of HIV seroconverters, HCV annual incidence was 0.3% in 1990, 1.3% in 2005 and 2.1% in 2015. In a second CASCADE study, in the first year after HIV diagnosis, annual HCV incidence in men was below 1% in men diagnosed with HIV between 1990 and 1999, and below 2% in those diagnosed between 2000 and 2009, but had jumped to over 4% in those diagnosed between 2010 and 2015. European data also shows a high rate of reinfection in HIV-positive men cured of HCV, in the order of 6.5% incidence of reinfection a year.
In contrast, HCV incidence in HIV-negative men is generally a lot lower, with a meta-analysis of studies showing a pooled incidence of 0.15% a year and with the highest incidence seen (in Taiwan) of about 0.4% a year.
There are some indications that HCV incidence might be somewhat higher than this in HIV-negative men participating in PrEP studies. HIV incidence in men in the PROUD and Ipergay studies and in the Kaiser Permanente PrEP cohort in northern California ranged from 0.7 to 1.3% a year.
However, we have no idea if this is likely to be seen in AmPrEP, or whether being on PrEP has any causal relationship with HCV infection. Wanting PrEP may simply be an indicator that the person is at high risk of both HIV and HCV infection.