HIV surveillance programs do not typically collect comprehensive data on antiretroviral therapy (ART). We validated a population-based measure of ART initiation that uses HIV viral load (VL) results in the absence of data on ART.
We used CD4/VL data reported to NYC HIV Surveillance for persons aged ≥13 years and diagnosed with HIV from 2006-2012 to validate estimates of ART initiation date based on three ART initiation definitions: 1) ≥1-log decline in copies/mL between two VLs over 3 months; 2) ≥2-log decline in copies/mL between two VLs over 3 months; 3) the earliest of either a ≥1-log decline in VL over 3 months, or a change from detectable VL to undetectable VL (<400 copies/mL) over any interval. We plotted median CD4 counts by quarter before and after ART initiation to compare estimated initiation date with nadir of the CD4 trajectory. RESULTS
A total of 24,348 persons were diagnosed with HIV in NYC from 2006-2012. 12,179 persons had probable ART initiation based on ≥1-log decline, 12,123 based on ≥2-log decline, and 14,311 based on ≥1-log decline or detectable-undetectable change. Lowest median CD4 count occurred at the estimated ART initiation date for all three definitions. The definition based on a ≥1-log VL decline or a change from detectable to undetectable VL captured more ART initiations and identified earlier initiation dates.
Serial VL measures are a valid source for estimating ART initiation. A definition that includes a ≥1-log VL decline or a change from detectable to undetectable VL performed best.