Background: Worldwide, HIV prevalence among transwomen is 50 times higher than in the general adult population. In many surveillance systems and surveys, transwomen and their male sexual partners are classified as “men who have sex with men” (MSM), irrespective of gender identity and sexual orientation. Little is known about how transwomen acquire HIV, which may be due in part to this misclassification as “MSM”. We sought insights on sexual and needle-sharing networks as potential sources of HIV among transwomen by examining phylogenetic transmission clusters. We also assessed a new transmission risk paradigm that re-classifies males closely linked to transwomen as non-MSM.
Methods: San Francisco residents diagnosed with HIV (2000-2015), in care at public facilities and with available viral pol sequences were included in the analysis. Transmission clusters with ≥2 cases were identified by bootstrap values ≥90% and mean pairwise genetic distances ≤0.025%.
Results: Transwomen were 275 of 5,200 cases with viral sequences; 86 transwomen were in 70 clusters; 44 (51%) had injection risk. Many clusters with transwomen contained MSM-persons who inject drugs (MSM-PWID) (47% of clusters) and non-MSM PWID (26%); whereas MSM were in 54% of clusters and heterosexual men in 1%. After re-classification, the profile of clusters shifted: 16% of clusters contained MSM-PWID, 57% had non-MSM PWID, 16% had MSM and 47% had heterosexual men. Similarly, among 130 clusters containing cis women, 27% had MSM-PWID, 41% had non-MSM PWID, 28% had MSM and 58% had heterosexual men.
Conclusions: Applying the new paradigm for classifying the transmission risk of transwomen and their partners suggests that transwomen may stand apart from the MSM epidemic. The risk profile of transwomen''s transmission clusters is highly sensitive to whether or not male partners are classified as MSM. Under the new paradigm, transmission clusters containing transwomen closely resemble clusters containing cis women, with a strong presence of PWID and heterosexual men. There is increasing recognition that transwomen should be considered by their gender identity for health services and research. The same consideration perhaps should apply to male sexual partners of transwomen. Examining transmission clusters may bring new insights to the applicability of MSM-focused research to transwomen and their partners.