New to cohort, not new to care: leveraging historical data in HIV clinical cohorts in the United States.

Identifying people with prior HIV care experience in clinical cohorts requires historical HIV data. We examined the availability of historical antiretroviral therapy (ART) prescriptions, historical CD4 counts, historical HIV viral loads, suppressed viral load at enrollment, and historical AIDS defining conditions in United States-based clinical cohorts in the North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD). At enrollment, we classified participants as new to care, transfer (without a gap in care), re-engaging in care (transfer after a gap in care), or previously in care with unknown transfer status. From 2000 to 2022, transfers increased from 30% to 68% while new to care declined from 31% to 21%. Historical ART prescriptions and suppressed viral load at enrollment became increasingly common data types for identifying prior HIV care, specifically after 2012. Among participants not new to care with ≥1 known historical HIV date, the median time between earliest known HIV date and enrollment increased from 1.9 years in 2000 to 5.6 years in 2022. While some data types may serve as practical proxies, we recommend that HIV cohorts systematically collect and assess all 5 data types to improve identification of participants new to care and adopt our algorithm specific to their context.