Increasing frequency and transmission of HIV-1 non-B subtypes among men who have sex with men in the Swiss HIV Cohort Study. Journal of Infectious Diseases
Duran Ramirez and Ballouz et al. assessed temporal trends and transmission dynamics of HIV-1 non-B subtypes – historically transmitted mainly through heterosexual contacts and among individuals of non-European origin – among men who have sex with men (MSM) in the Swiss HIV Cohort Study.
All cohort participants who had acquired HIV through MSM contacts and with available HIV genotype information were included. Temporal trends of the prevalence of non-B subtypes among MSM newly diagnosed with HIV-1 were assessed, and molecular clusters analysed to characterize transmission.
The study included 5’114 MSM with a median age of 35 years (IQR 29-43). Most individuals were of white ethnicity (4’541, 88.8%) and presented with a median CD4 cell count of 380 cells/µL (IQR 216-531) at the time of HIV diagnosis. Authors observed a marked increase in the proportion of non-B subtypes among MSM from 0% (0/123) in 1990 to 1% (9/113) in 2000, 10% (19/187) in 2010 and 34% (11/32) in 2019. HIV subtypes A and CRF02_AG accounted for the largest proportion of the increase. In comparison to individuals who acquired HIV through heterosexual contacts, larger molecular transmission clusters with mainly European individuals were present among the MSM population.
In conclusion, the study shows a substantial increase in non-B subtype transmission among MSM with newly diagnosed HIV in Switzerland. The largest increase was found in subtypes which are predominant in Western Europe, with transmission clusters mainly identified among European individuals. Taken together, these findings indicate that the increased circulation of non-B subtypes may be mainly due to ongoing domestic transmission within the Swiss MSM population.