Among men who have sex with men (MSM) in Switzerland, both domestic and international transmission of hepatitis C virus (HCV) infection have contributed significantly to the HCV epidemic, according to results published in the Journal of Infectious Diseases.

The results indicate that local transmission has become the dominant source of infection over time.

The study included HCV subtype 1a genomes from participants from the Swiss HIV Cohort Study who were diagnosed with replicating infections between 1999 and 2016 (N=99). Of the genomes, 66 were from MSM.

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The researchers performed sequencing on the HCV genomes. They inferred maximum-likelihood phylogenetic-trees and time-trees containing a fragment of the NS5B region of these and other 374 circulating strains from national and international databases. Using the trees, the researchers inferred transmission clusters and considered the country composition of the clusters to determine whether the infections were domestically or internationally transmitted.

Of the MSM sequences, 60 were located within 14 MSM transmission clusters and 12 transmission pairs. Of these, 50% (n=30) were located in cluster C1, which consists of predominantly Swiss and German sequences. Another 18% (n=11) were located in cluster C2, which consists of predominantly Swiss and British sequences. Overall, the researchers determined that 50% of Swiss MSM sequences were located in Swiss-only clusters or transmission pairs.

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The results indicated that between 2000 and 2007, the percentage of infections attributable to domestic transmission was 54%; this increased to 85% between 2008 and 2016.

“Swiss-domestic HCV transmission among MSM has grown over time,” the researchers wrote. “This implies that intensive test-and-treat interventions at the national level are likely to succeed.”


Salazar-Vizcaya L, Kouyos RD, Metzner KJ, et al. Changing trends in international versus domestic HCV transmission in HIV-positive MSM: a perspective for the DAA scale-up era [published online February 13, 2019]. J Infect Dis. doi: 10.1093/infdis/jiz069

This article originally appeared on Infectious Disease Advisor