Background: Surveillance of HIV-1 drug resistance in antiretroviral-treated patients is important from the public health perspective of the spread of resistance and to evaluate the proportion of patients for whom new drugs are needed.
Methods: Patients were consecutively included in 28 centers in France and 1 center in Switzerland if they had a viral load measurement performed in June 2004, with a result >or=1,000 copies/mL. Reverse transcriptase, protease, and gp41 genes were sequenced, and resistance mutations were reported as listed on the Web site ( www.iasusa.org). The genotypic resistance results were interpreted by the Agence Nationale de Recherches sur le SIDA et les Hepatites Virales (ANRS) and Stanford algorithms.
Results: The 498 patients included had been exposed to 9 (interquartile ratio [IQR]: 6 to 12) antiretroviral drugs. Patients' viruses harbored 4 nucleoside reverse transcriptase inhibitor (IQR: 1 to 6) and 4 protease inhibitor (PI; IQR: 2 to 8) resistance mutations, whereas 44% had at least 1 nonnucleoside reverse transcriptase inhibitor resistance mutation. The frequency of resistance to at least 1 drug was 88% with the ANRS algorithm and 83% with the Stanford algorithm. The frequencies of complete resistance to 1, 2, and 3 classes of drugs were 37%, 15%, and 4%, respectively, with the ANRS algorithm and 27%, 23%, and 24%, respectively, with the Stanford algorithm. The most important differences between algorithms were for PIs. Using the ANRS algorithm and extrapolation on the whole French database, 19% of all treated patients could contribute to the spread of resistance and 4% had complete resistance to 2 classes of antiretroviral drugs.
Conclusions: The observed patterns of resistance are linked to a long-lasting history of antiretroviral therapy. The frequency of multiresistance can vary according to the interpretation systems.