LAUSR

We aimed to describe transitions between preexposure prophylaxis (PrEP) eligibility and HIV infection among HIV-negative men who have sex with men (MSM). We used data from 1885 MSM, who had not used PrEP, enrolled in the Lisbon Cohort of MSM with at least 2 consecutive measurements of PrEP eligibility from 2014 to 2020. A time-homogeneous Markov multistate model was applied to describe the transitions between states of PrEP eligibility-eligible (E) and ineligible (I)-and from these to HIV infection (HIV). The intensities of the transitions were closer for I-E and E-I (intensities' ratio, 1.107 [95%CI, 1.008-1.176]), while the intensity of the E-HIV transition was higher than that for ineligible-HIV infection (I-HIV) (intensities' ratio, 9.558 [95%CI, 0.738-65.048]). The probabilities of transitions increased with time; for 90 days, the probabilities were similar for the transitions I-E and E-I (0.285 [95%CI, 0.252-0.319] vs 0.258 [95% CI, 0.228-0.287]), while the transition E-HIV was more likely than I-HIV (0.004 [95%CI, 0.003-0.007] vs 0.001 [95%CI, 0.001-0.008]) but tended to become closer with time. Being classified as ineligible was a short-time indicator of a lower probability of acquiring HIV. Once an individual moved to eligible, he was at a higher risk of seroconversion demanding a timely delivery of PrEP.