Original research article Superimposing incident sexually transmitted infections on HIV phylogram to investigate possible misclassification of men who have sex with men as heterosexuals in a cohort in Antwerp, Belgium Kara K Osbak 1 , Conor J Meehan 2 , Sergio G Ribas 1 , Leo Heyndrickx 1,2 , Kevin K Ari € en 2 , Achilleas Tsoumanis 1 , Eric Florence 1 , Marjan Van Esbroeck 1 , Katrien Fransen 1 and Chris R Kenyon 1,3 Abstract In this study, we assessed if the superimposition of incident sexually transmitted infections (STIs) on HIV phylogenetic analyses could reveal possible sexual behaviour misclassifications in our HIV-infected population. HIV-1 sequences collected between 1997 and 2014 from 1169 individuals attending a HIV clinic in Antwerp, Belgium were analysed to infer a partial HIV transmission network. Individual demographic, clinical and laboratory data collected during routine HIV follow-up were used to compare clustered and non-clustered individuals using logistic regression analyses. In total, 438 (37.5%) individuals were identified in 136 clusters, including 76 transmission pairs and 60 clusters consisting of three or more individuals. Individuals in a cluster were more likely to have a history of syphilis, Chlamydia and/or gonorrhoea (P < 0.05); however, when analyses were stratified by HIV transmission risk groups (heterosexual and men who have sex with men [MSM]), this association only remained significant for heterosexuals with syphilis (P ¼ 0.001). Under closer scrutiny, this association was driven by six heterosexual men who were located in six almost exclusively MSM clusters. A parsimonious conclusion is that these six individuals were potentially misclassified as heterosexual. Improving the accuracy of sexual behaviour reporting could improve care. Keywords HIV epidemiology, HIV infection, men who have sex with men, sexually transmitted infections, molecular epidemiology, syphilis Date received: 29 June 2018; accepted: 30 November 2018 Introduction Phylogenetic analysis of HIV sequences passively accu- mulated through routine drug resistance testing (DRT) can provide useful insights into local HIV transmission network characteristics when coupled with demograph- ic, clinical and sexually transmitted infection (STI) data. These approaches have proven useful in highlighting HIV transmission networks at various geographical levels, 1–3 thereby allowing the identification of hotspots within (sub)populations such as men who have sex with men (MSM). 4 A recent Belgian study by Chalmet et al. 1 1 Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium 2 Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium 3 Division of Infectious Diseases and HIV Medicine, University of Cape Town, Cape Town, South Africa The first two authors contributed equally to this work. Corresponding author: Kara K Osbak, Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Institute of Tropical Medicine, Nationale straat 155, Antwerp 2000, Belgium. Email: kosbak@hotmail.com International Journal of STD & AIDS 2019, Vol. 30(5) 486–495 ! The Author(s) 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0956462418821752 journals.sagepub.com/home/std