Selection by indication of potent antiretroviral therapy use in a large cohort of women infected with human immunodeficiency virus

To characterize selection factors related to therapy initiation, the authors investigated the extent to which key markers of human immunodeficiency virus (HIV) disease severity were associated with initiation of potent antiretroviral therapy (ART). Logistic regression was used to determine the effects of CD4⁺ cell count and HIV RNA level on potent ART initiation during 6-month periods among 2,059 HIV-infected US women enrolled in the Women's Interagency HIV Study. Low CD4⁺ counts and high HIV RNA levels were significantly (p < 0.05) associated with initiation of potent ART. During all periods between April 1996 and March 1998, CD4⁺ counts were more strongly associated with potent ART initiation than HIV RNA levels were; however, during the last period, both were associated (odds ratio per 100 CD4⁺-count decrease = 1.17, p < 0.01; odds ratio per 1 log₁₀ increase in HIV RNA level = 1.48, p < 0.05). For a CD4⁺ count of 500 cells/ml and an HIV RNA level of 5,000 copies/ml, the probability of potent ART initiation increased from 0.5% to 16.8% between October 1995-March 1996 and October 1997-March 1998, suggesting earlier initiation of potent ART. Given the documented occurrence of confounding by indication, prospectively collected, time-dependent data on markers of disease progression and therapy use should be considered when making population-level comparisons before and after introduction of potent ART.