Objectives: To identify trajectories of chemsex engagement and their evolution across time among men who have sex with men (MSM) and the associated factors.
Methods: Among 2518 PrEP-using MSM in the French ANRS- Prévenir cohort, a group-based trajectory model was used to identify trajectories of chemsex engagement. A multivariable model was then used to estimate time-constant factors associated with trajectory membership, and time-varying factors associated with the shape of each trajectory. Data were collected quarterly from self-administered online questionnaires and electronic case record forms. The median follow-up time was 21 months [interquartile range: 9-27 months].
Results: Four distinct trajectories were identified: the Null/low (probability of engagement) (N-CX, n = 1881, 75%), the Increasing (I-CX, n = 158, 6%), the Decreasing (D-CX, n = 195, 8%), and the High (H-CX, n = 284, 11%). Compared to N-CX: MSM in the I-CX and D-CX were younger (OR [95%CI]: 0.95[0.93-0.98], p < 0.001 & 0.94[0.91-0.96] p < 0.001 per additional year or point (p/y), respectively), while MSM in the H-CX were older (1.03[1.01-1.05] p/y, p = 0.016); depression score was higher among the D-CX (1.02[1.00-1.04] p/y, p = 0.026) and lower among the I-CX (0.97[0.94-0.99] p/y, p = 0.028). Use of daily PrEP regimen (compared to 'on-demand') was associated with increased and decreased likelihood of chemsex engagement for the H-CX (Coeff.(SE): 0.75(0.33), p = 0.027) and D-CX (-0.41(0.20), p = 0.043), respectively. The likelihood of chemsex engagement increased for the D-CX (0.02(0.01), p = 0.006), H-CX (0.04(0.01), p = 0.004), and N-CX (0.008(0.003), p = 0.011) as their number of casual sex partners increased. Participants in the N-CX and D-CX were more likely to engage in chemsex if they engaged in condomless anal sex during their last sexual encounter [0.86 (0.34), p = 0.011 and 1.63 (0.21), p < 0.001, respectively].
Conclusion: Four different patterns of engagement in chemsex were identified, with specific sexual behaviors and HIV prevention strategies. Differentiated healthcare and prevention approaches could be offered to MSM based on their patterns of chemsex engagement. [Author's abstract]