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Background:  Antiretroviral regimens may vary in ability to suppress viral load  in people infected with different HIV subtypes due to differences in resistance development. Subtype B is most prevalent in Europe and United States where antiretrovirals have predominantly been developed but non-B subtypes are increasing through travel and migration. This study compares response to therapy amongst patients with different subtypes in Europe.

Methods:  We determined the subtype (73% by phylogenetic analysis) of 635 EuroSIDA patients prior to starting HAART (≥ 3 drugs including 2 nucleoside reverse transcriptase inhibitors [NRTI] and protease inhibitor [PI]/non-NRTI [NNRTI]/abacavir) with no prior PI/NNRTI/abacavir use and baseline viral load of > 500 copies/mL. Virologic response to HAART (whether or not first viral load measured 6 to 12 months from start of HAART was ≤ 500 copies/mL) was analyzed via logistic regression to compare B- and non-B-infected patients. Stratification of non-B subtypes was also investigated.

Results:  Of the 635 patients, 505 (80%)were infected with subtype B. Median dates of starting HAART were April 1998 and May 1997 for B and non-B, respectively, p < 0.001. Baseline viral load (4.7 log₁₀ copies/mL for both) and CD4 counts (249 and 227 cells/mm³) were similar, as was the type of HAART regimen; > 50% started single PI regimens; 55% of B and 48% of non-B were antiretroviral-naïve at baseline, p = 0.15. Treating missing values of viral load as virologic failures, subtype-B patients had the lowest response rate with 59% achieving successful virological response compared to 64% of non-B, p = 0.28 (excluding missing values gave similar results with n = 451 for B, n = 122 for non-B). Response rates in non-B subtypes were:  57% A (n = 75), 71% C (n = 24), 74% “other” (n = 31). After adjustment for date starting HAART, risk group, baseline CD4 nadir, viral load, hepatitis B/C status, age, antiretroviral-naïve or not, number of new drugs and regimen type, no significant difference was found in response between subtype B (reference) and non-B, odds ratio (OR) 1.32 (95% CI 0.83 to 2.10), p = 0.25. Likewise in A, C, and “other” subtypes compared with B, no significant differences were found, adjusted OR:  1.10 (0.63 to 1.91), p = 0.75; 1.77, (0.64 to 4.85), p = 0.27; 1.88 (0.74 to 4.76), p = 0.18, respectively.

Conclusions:  There was no evidence that non-B-infected patients were less likely to achieve a successful virologic response to HAART. Further stratification by A and C subtypes also did not suggest a detrimental outcome compared with B. The continued expansion of EuroSIDA data will allow more sensitive analyses in the future.

Keywords: Subtypes; HAART; Virological Response