Background:  We examined the prevalence and prognostic value of discordant immunologic and virologic responses to HAART among community-based injecting drug users (IDU) in Baltimore, Maryland.

Methods:  In a cohort evaluated semi-annually since 1988, we examined patients reporting initial HAART use from 1996-2000. Virologic (HIV RNA <1000 copies/mL) and immunologic (CD4 >500 cells/ml or increase of 50 cells/mL from HAART initiation) responses were examined in the first years of HAART. Cox regression was used to examine the effect of early response on progression to new AIDS diagnosis or AIDS-related death. 

Results:  Among 265 HAART initiators, median age was 43 years, 71% were male and 94% African American. In the first year, 92 (35%) had both virologic and immunologic response, 55 (21%) had immunologic response only, 42 (16%) had virologic response only, and 76 (29%) had no response. Compared to nonresponders, those with any response had higher pre-HAART CD4 (p = 0.03) and lower HIV RNA (p = 0.07). Persons with CD4 response were also significantly less likely to report current IDU (38%) than those without CD4 response (53%, p = 0.01). Compared to non-responders (9%) and those with discordant responses (20% and 15%), subjects with early combined response were more likely to have combined response in the second year (43%). However, only 48% were still on HAART 2 years after initiation. AIDS-free survival proportions 4 years after HAART initiation were 64% for subjects with no response in the first year, 90% for subjects with combined response and 83% for those with discordant immunologic/virologic response (p <0.001). After adjusting for pre-HAART CD4, compared to non-responders, those with combined response had significantly reduced risk of progression (relative hazard [RH] 0.2; 95%confidence interval [CI] 0.1 to 0.4). Those with only immunologic (RH 0.5; 95% CI 0.2 to 0.9) and virologic response (RH,0.5; 95% CI,0.3-1.0) had reduced risk of progression compared to non-responders but experienced faster progression than those with a combined response.   

Conclusions:  Early discordant virologic and immunologic responses were common in this population. In contrast to reports from other cohorts, progression rates for discordant groups did not differ substantially by whether early response was immunologic or virologic. Despite low rates of sustained HAART responses beyond the first year and high rates of HAART discontinuation, early virologic and immunologic response conferred substantial survival benefit.