Determinants of HIV-1 transmission clusters and transmitted drug resistance in men who have sex with men: A multicenter study in Portugal (2014-2019)

Introduction: In the EU/EEA, men who have sex with men (MSM) is a priority group for the prevention and control of HIV-1 infection. In Portugal, the 2023 HIV incidence rate was 8.2 per 100,000 inhabitants, with 876 new infections, 41.7% in MSM. We aim to characterize HIV-1 transmission clusters (TC) and transmitted drug resistance (TDR) and its sociodemographic, behavioral, clinical, and viral genomic determinants in MSM newly diagnosed in Portugal between 2014 and 2019. Methods: A total of 340 MSM newly diagnosed with HIV-1 infection at 17 hospitals in Portugal were included. TC was identified with branch support ≥90% and 1.5% genetic distance. Logistic regression models were used to examine factors associated with TC and TDR. Results: We identified 38 TC with 104 MSM, which includes 81 (26.6%) of the 305 MSM from our sample included in cluster analysis. The overall prevalence of TDR was 8.2%. Only HIV-1 subtype C was significantly associated with TDR. Overall, 10.5% of the clusters had at least 1 surveillance drug resistance mutation. There was no significant difference in the prevalence of TDR or the proportion of Portuguese and migrant MSM inside and outside clusters. Age at diagnosis, district of residence, unprotected sex with a woman, HIV testing, presenter status, and HIV-1 subtype were significantly associated with TC. Conclusion: Specific subgroups of MSM are contributing to HIV-1 clustered transmission in Portugal. However, no association was found between TDR and sociodemographic or behavioral factors. Directed prevention measures should focus on those subgroups.