Using longitudinally sampled viral nucleotide sequences to characterize the drivers of HIV-1 transmission. HIV Medicine
Reichmuth et al. aimed to develop and to test a molecular epidemiology method based on phylogeny reconstruction and cluster analysis to characterize potential HIV-1 transmitters and understand the drivers of the HIV-1 epidemic in Switzerland. This method was developed and validated using longitudinally sampled HIV-1 partial polymerase (pol) nucleotide sequences, routinely and retrospectively obtained, in the drug resistance database (DRDB) of the Swiss HIV Cohort Study (SHCS).
The proposed method was able to identify 279 potential HIV-1 transmitters and allowed the authors to determine the main epidemiological and virological drivers of transmission. They found that the directionality of transmission was consistent with infection times for 72.9% of 85 potential HIV-1 transmissions with accurate infection date estimates. Being a potential HIV-1 transmitter was associated with risk factors including viral load [adjusted odds ratiomultivariable (95% confidence interval): 1.86 (1.49–2.32)], syphilis coinfection [1.52 (1.06–2.19)], and recreational drug use [1.45 (1.06–1.98)]. By contrast for the potential HIV-1 recipients, this association was weaker or even absent [1.18 (0.82–1.72), 0.89 (0.52 –1.55) and 1.53 (0.98–2.39), respectively], indicating that inferred directionality of transmission is useful at the population level.
In conclusion, identifying drivers of HIV-1 transmission by not only identifying transmission clusters but also characterizing individuals who may have potentially transmitted HIV-1 is of great importance for understanding the drivers of the HIV-1 epidemic. The associated risk factors at an individual level are crucial to better understanding the dynamics and mechanisms of an HIV-1 epidemic and will help to tackle the various ongoing epidemics at the population level, but in a more individualized manner. The proposed method was validated using the densely sampled setting of the SHCS as a case study. This lays the groundwork to study evolution and transmission of HIV-1, as well as the risk factors of HIV-1 transmitters, and allows large transmission clusters to be characterized.