Competing risks of AIDS and death in people living with HIV: a left-truncated and right-censored retrospective cohort study in Khuzestan, Iran (2001–2022)

OBJECTIVE: This study aimed to estimate the risks of AIDS progression and death among people living with HIV using left-truncated and right-censored survival methods. Competing-risk methods were used to evaluate AIDS progression in the presence of death as a competing event. METHODS: A retrospective cohort study was conducted using data from Behavioral Disease Counseling Centers (BDCC) in East Khuzestan, Iran, from 2001 to 2022. Survival analyses were performed within a left-truncated and right-censored framework, in which the physician-estimated HIV infection date served as the biological time origin and HIV diagnosis was treated as delayed entry. Competing-risk methods were used to evaluate AIDS progression in the presence of death as a competing event. Late HIV diagnosis, defined as a baseline CD4 count below 350 cells/mm³, was a key variable of interest. RESULTS: Throughout the follow-up period, the cumulative incidence of death exceeded that of AIDS in most time intervals. Late diagnosis was associated with significantly higher hazards for both death and AIDS, with a two-fold increase in the hazard of death (HR = 2.1, p < 0.001). Other significant predictors of death included age ≥ 50 (HR = 2.4, p < 0.001), male sex (HR = 2.84, p = 0.014), and TB co-infection (HR = 2.02, p < 0.001). CONCLUSION: Accounting for left truncation and right censoring is essential when analyzing registry-based HIV cohorts. Late HIV diagnosis was strongly associated with increased risks of both AIDS progression and death, highlighting the importance of earlier testing, timely diagnosis, and prompt linkage to care. Appropriate survival methods that accommodate delayed entry and competing risks can provide more accurate estimates of disease progression and mortality in HIV populations.