Men who have sex with men newly diagnosed with HIV-1 in Portugal (2023–2024): a comparative analysis of transmission clusters between migrants and non-migrants

Migration to Europe has been rising in recent years and is associated with higher HIV vulnerability due to overlapping social and structural barriers. New cases among migrants have been steadily increasing, and for the first time in Portugal, there were more cases among migrants than among non-migrants in 2023. This study aims to compare sociodemographic, behavioural, clinical, and viral genomic characteristics of non-migrant and migrant MSM newly diagnosed with HIV-1 in Portugal (2023-2024), as well as the composition of Transmission Clusters (TC) to which they belong. Between June 2023 and December 2024, 60 MSM were recruited upon HIV-1 reactive screening in a community centre in Lisbon. Sociodemographic and behavioural data were collected through a questionnaire. A blood sample was collected for viral load measurement and HIV-1 genomic sequencing. TC were identified using a branch support ≥ 90% and iterating between 1.5%, 2.5%, 3.5%, 4.5%, 5.5% and 6.5% genetic distances. Among the 60 MSM newly diagnosed with HIV in our 2023-2024 community-based sample, 70% were migrants, of whom 60% were from Latin America and 10% from other regions. The results showed significant differences in age at diagnosis, district of residence, and HIV-1 subtype between non-migrants and migrants, while sexual behaviours, testing patterns, and STI prevalence were similar across the two groups. No difference between the proportion of non-migrant and migrant MSM in TC was found. Notably, phylogenetic analysis suggests that migrant MSM are mainly related to other migrant MSM and outside Portugal. In contrast, non-migrant MSM were more frequently found in mixed clusters. All Surveillance drug resistance mutations (SDRM) in TC were related to migrant MSM. Findings from this single community-based centre suggest that recent HIV-1 epidemiology among MSM has shifted towards an increased proportion of migrants in MSM HIV diagnosis, who are primarily involved in sexual networks with other migrants. To effectively address these current dynamics, Portugal should explore strategies to improve early and accessible PrEP, STI, and HIV testing for the migrant MSM communities.