Virological failure among patients on HAART from across Europe: results from the EuroSIDA study

Objectives: To monitor the response to highly active antiretroviral therapy (HAART) over time and the proportions of patients with poor virological co ntrol in order to help provide some insight into drug resistance. Design: Analysis of data from the EuroSIDA study; an observational study in itiated in 1994 of almost 8500 patients with HIV from across Europe. Methods: Patients who initiated HAART, and had both a CD4 lymphocyte count and viral load measured in the 3 months prior to starting HAART, were inclu ded in analyses. The proportion of patients with a poor virological respons e (defined as a viral load of >10 000 copies/ml, using either a single meas ure or two consecutive measures) at 16 and 48 weeks was determined. Multiva riate logistical regression was used to determine the factors associated wi th a poor virological response at both time points. Results: Median CD4 cell count at starting HAART was 218 cells/mm(3) [inter quartile range (IQR), 113-327 cells/mm(3)] and median viral load was 4.36 l og(10) copies/ml (IQR, 3.57-5.04 log(10) copies/ml). At 16 weeks, 16% had a viral load of >10 000 copies/ml based on a single viral load measure and 1 0% if the more stringent definition of two consecutive viral loads above th is level was used. At 48 weeks these proportions were 19% and 13%, respecti vely. Compared with patients from Southern Europe, patients from both Centr al and Northern Europe had approximately half the chance of a poor virologi cal response at 16 weeks (odds ratios 0.53 and 0.47, P=0.0015 and P<0.0001, respectively), while at 48 weeks both regions still had approximately a 25 % reduced chance of a poor virological response, but this was no longer sta tistically significant (odds ratio 0.77 and 0.75, P=0.17 and P=0.13, respec tively). Conclusions: There were marked differences in virological response to HAART across regions of Europe, which may be partly explained by regional differ ences in access to HAART and utilisation. If drug resistance is closely rel ated to virological failure, these results may help to provide an early ins ight into the potential problem of drug resistance across Europe. Continued follow-up is essential to monitor patients with poor virological control.