Wang L, Krebs E, Min JE, et al. - Using a continuous-time, multistate Markov model, researchers determined the monthly probabilities of on-antiretroviral therapy (ART) CD4 T-cell count progression, mortality, ART dropout, and ART re-initiation in this study. In addition, they validated health-state transition probability estimates to ensure accurate reproduction of the regional HIV micro-epidemics across the United States. They considered a consortium of 17 adult and pediatric HIV-care providers located in the northeastern (n = 8), southern (n = 5), and western (n = 4) regions of the United States. A total of 32,242 individuals were included; among these, ART interruption was reported in 8,614, and death was reported for 1,325 over a median follow-up of 4.9 years. According to findings, disease progression during ART and probability of ART retention across race and ethnicity, HIV risk groups, and regions may be heterogeneous. The investigators noted greater increases in CD4 cell counts in women, men who have sex with men, and individuals with no previous ART experience, whereas increased probabilities of ART dropout and faster disease progression were noted in black individuals and those who inject drugs. Hazard for ART dropout was higher for individuals who were from the south or the west of the United States vs individuals from the northeast. This was noted regardless of CD4 strata.