A2 Phylogenetic investigation of transmitted HIV-1 drug resistance mutations in Denmark, 2009–17

Transmission of HIV-1 resistance mutations among therapy-naïve patients impairs the efficiency of antiretroviral therapy (ART). Therefore, genotypic resistance testing of patients is recommended at baseline, as this both allows for the selection of the correct ART regimen and for surveillance of transmitted drug resistance mutations (TDRM) among therapy naive HIV-1 patients. In Denmark, the occurrence of TDRM in newly diagnosed and therapy naïve HIV-1 patients is monitored through the SERO project. Here, we investigated if the prevalence of TDRM differed between patients within and outside of phylogenetically identified transmission clusters. Samples from 1,227 newly diagnosed HIV-1 patients were sent along with epidemiological information to the Virological Surveillance and Research group at Statens Serum Institut. HIV-1 RNA extraction, RT-PCR and Sanger sequencing of the pol gene was performed using an in-house assay. The sequences were analyzed using BioNumerics v. 6.6 and manually checked for the presence of mixed mutations and analyzed for mutations using the HIVDB 8.4 algorithm implemented at the Stanford database. Sequence alignments were performed in Mafft, and phylogenetic analysis was performed using Mega 6.0 using the Maximum likelihood general time reversible model with 100 bootstrap replicates. Clusters were identified with ClusterPicker at default settings (cluster support = 90%, genetic distance 4.5%). Active clusters contained newly diagnosed patients from the 2015 to 2017 period. HIV-1 sequences from 588 patients belonged to one of 154 clusters, and sequences from 639 patients did not belong to a cluster. Patients in clusters were significantly more likely to be men who have sex with men and subtype B and significantly less likely to be late presenters (Fisher’s test P < 0.05). The TDRM prevalence was significantly higher for patients outside of clusters than within clusters, 16.6 per cent versus 12.1 per cent, respectively (Fisher’s test P < 0.05); however, no significant differences were found in the TDRM prevalence between the 75 active and 79 inactive clusters, nor between small (<3 patients) and large (≥3 patients) clusters. E138A, V179D, and K103N were the three most prevalent TDRMs for both patient groups, whereas M41L differed between them. In Denmark, the TDRM prevalence is lower within clusters than outside, indicating that TDRM cases are either imported and/or belong to yet unidentified clusters.