A21 HIV-1 sub-subtype F1 outbreak among MSM in Belgium

Abstract

HIV-1 non-B subtype infections have been observed in Belgiumsince the 1980s. However, subtype B predominates amongstmen having sex with men (MSM), whereas other subtypes aremainly associated with sub-Saharan African migrants and heterosexual risk behavior. In the last decade, subtype F1 diagnoseshave increased substantially in Belgium, representing 9% ofnewly diagnosed and therapy-naïve HIV-1 patients linked tocare in 2014. In the present study, the Belgian subtype F1 epidemic has been characterized within a global context, where F1is responsible for <1% of HIV-1 infections. The Belgian AIDSReference Laboratories collected HIV-1 pol sequences frompatients linked to care and sub-subtype F1 was verified usingRega v3 and COMET v1.0 subtyping tools. Concordant F1sequences were retained from 293 patients, who were diagnosed with HIV-1 between 1988 and 2015. The number of F1diagnoses increased from three in 2001-2 to 83 in 2013-4.Seventy-seven percent were men, with 52% homosexual, 15%bisexual, and 15% heterosexual contact as the probable transmission route (18% not registered). Belgium was the probablecountry of infection for 54% of the patients, whereas for 38%this information was not registered. A reference dataset fromcountries with a high burden of F1 infections or with a potentialrole in the global origin of sub-subtype F1 was collected frompublic and private databases and the phylogeny was reconstructed using RAxML and BEAST. These analyses indicate that190 Belgian F1 sequences, 97% from men, and 72% with homosexual/bisexual risk behavior (17% not registered), belong to amonophyletic group with two sub-clades. Together with aSpanish clade, the Belgian clade is embedded in the Braziliansubtype F1 diversity and probably emerged after single or twomigration events from South-America with one dead-end lineage (2 strains) and one actively spreading cluster (188 strains).This study reconstructed the structure of the local HIV-1 F1 epidemic and showed that onward transmission of subtype F1occurs extensively among MSM. It illustrates the introductionand dissemination of strains in one geographically restrictedrisk group in which the subtype was previously absent.