Estimating HIV-1 drug resistance in antiretroviral-treated individuals in the United Kingdom.

Good estimates of the prevalence of human immunodeficiency virus drug resistance are important for assessing requirements for new drug classes and modeling the spread of resistance. However, little consensus exists on optimal methodologies to generate such data. To compare methodologies, we used the national data set of resistance tests from >4000 patients in the United Kingdom performed between 1998 and 2002. When single-time-point analysis (method 1) was used, the proportion of tests with any form of resistance was approximately 80%, with little time trend. When a cumulative model of resistance (method 2) was used and placed in the context of all treated patients, the prevalence of any resistance increased by year, reaching 17% of treated patients in 2002. Method 2 also nearly doubles estimates of numbers of individuals infected with multiclass drug-resistant virus. Our results identify an urgent need for new drugs within existing classes and new classes of antiretroviral therapy.