GB virus C (GBV-C) infection is associated with delayed mortality in HIV-infected people in most, but not all, studies. Previous investigations of the effect of GBV-C viraemia on response to antiretroviral therapy (ART) were inconclusive. To determine the effect of GBV-C on ART, we retrospectively analysed plasma samples taken from patients in a prospective randomized clinical trial of ART in HIV-positive Brazilians.
GBV-C viraemia was characterized by testing stored serum samples from 175 participants by reverse transcriptase-polymerase chain reaction (RT-PCR). Subjects were randomized to receive indinavir (n=59), zidovudine and lamivudine (n=58), or zidovudine, lamivudine and indinavir (n=58). The effect of GBV-C viraemia on the average change in HIV viral load and CD4 count following initiation of therapy was evaluated in a multiple regression analysis.
The prevalence of GBV-C viraemia was similar to that observed in previous studies (24%). HIV viral load decreased following ART to a significantly greater extent in patients with GBV-C viraemia (by 0.48 log(10) HIV-1 RNA copies/mL, P=0.009, adjusting for age, ART group, and baseline CD4 count). Although there was no significant difference in change in CD4 count between individuals with and without GBV-C viraemia overall, CD4 counts were higher following 48 weeks of therapy in GBV-C viraemic individuals receiving the least potent ART regimen (zidovudine and lamivudine) compared with those without GBV-C infection.
GBV-C viraemia is associated with an enhanced reduction of HIV viral load in response to ART. In this study of treatment-naive individuals during 48 weeks of follow up, patients with GBV-C viraemia had reductions in HIV viral load that were approximately 0.5 log copies/mL greater than those found in patients without GBV-C viraemia. This is similar to reductions observed with nucleoside reverse transcriptase inhibitors.