Phylogenetic cluster analysis identifies virological and behavioral drivers of HIV transmission in MSM. Â Â Clinical Infectious Diseases.
Bachmann et al. aimed to investigate the impacts of treatment as prevention (TasP) and the potentially increased risk behavior on HIV transmission in men who have sex with men (MSM) at both the individual and population levels. Using the comprehensive Swiss HIV Cohort Study and its drug-resistance database, the authors reconstructed phylogenetic trees for each year between 2007 and 2017. They identified HIV transmission clusters dominated by MSM and determined their annual growth.
Both infectivity and behavioral risk scores were significantly higher in growing MSM transmission clusters compared to nongrowing clusters (P≤ .01). The fraction of transmission clusters without infectious members acquiring new infections increased significantly over the study period. The infectivity score was significantly associated with per-capita incidence of MSM transmission clusters in 8 years, while the behavioral risk score was significantly associated with per-capita incidence of MSM transmission clusters in 3 years.
In conclusion, this study demonstrates a new method to track the epidemiology of HIV, hereby identifying hotspots of ongoing transmission among MSM. The identified high-risk clusters could be used to target social networks harboring undiagnosed individuals spreading HIV. In these social networks, intensification of prevention is likely to have the largest impact. The significantly increasing number of new infections within transmission clusters without infectious members indicates a relative shift of epidemiological importance from diagnosed to undiagnosed individuals as drivers of the epidemic. Furthermore, this highlights the need for additional efforts to identify infectious individuals as early as possible and to link them into care. This method combining phylogenetics, clinical data, and behavioral data sheds light on high-risk social networks, where prevention and HIV testing should be intensified, and may thus inform the optimal allocation of resources for ending HIV transmission.