Prevalence of genotypic resistance among antiretroviral drug-naive HTV-1-infected patients in Belgium

Objectives: To estimate the prevalence and the evolution over time (1995-19 98) of genotypic resistance to antiviral drugs in antiretroviral drug-naive HIV-1-infected patients in Belgium. Design: Belgian Aids Reference Laboratories provided retrospective samples and clinical data from antiretroviral drug-naive HIV-l-infected patients wh o visited the hospital for the first time in 1995 (n=45), 1997 (n=75) and 1 998 (n=111). Genotypic resistance to the three available classes of drugs w as monitored using the Line Probe Assay (Innogenetics, Gent, Belgium). Addi tionally, ARMS-151 was performed for scoring multinucleoside resistance. Results: The prevalence of genotypic resistance at baseline to nucleoside a nalogue reverse transcriptase inhibitors (NRTls) and non-nucleoside reverse transcriptase inhibitors (NNRTls) were each between 10% and 20% for 1995, 1997 and 1998 without an increasing trend over time. For NRTls, resistance mutations were mainly related to zidovudine in 1995, whereas in 1997 and 19 98 baseline resistance was scored for zidovudine, lamivudine or for both dr ugs simultaneously. No patients displayed the multi-nucleoside resistance Q 151M mutation. Baseline resistance mutations to protease inhibitors (Pls) d id not rise significantly: 4.4% in 1995, 8% in 1997 and 9.9% in 1998. When scoring any resistance-related mutation, 26.6% displayed genotypic baseline resistance in 1995, 26.6% in 1997 and 31.5% in 1998. Discussion: The prevalence of genotypic baseline resistance to any drug, as scored with LiPA, in naiveHIV-1 patients in Belgium is 29%, with baseline resistance mutations to one or several drugs from all available classes of antiviral drugs. The ability of LiPA to pick up minor variants could be an explanation for the higher overall prevalence we observe, when compared to recent estimates in other countries of 16.3% and 22%, which were based on s equencing methods. According to the European guidelines for resistance test ing, resistance testing in Belgium before starting antiviral therapy should be considered.