HIV Digest	HIV Digest Archive

Among persons in North America who are newly infected with HIV, the prevalence of transmitted resistance to antiretroviral drugs has been estimated at 1 to 11 percent. In a recent study, researchers determined the prevalence of such resistance in a retrospective analysis of susceptibility to antiretroviral drugs before treatment and drug-resistance mutations in HIV plasma samples from 337 subjects with primary HIV infection who had not yet received treatment between May 1995 and June 2000 in 10 North American cities. Responses to treatment could be evaluated in 202 subjects.

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Over the five-year period, the frequency of transmitted drug resistance increased significantly between the two groups of patients divided according to date of diagnosis (1995-1998 and 1999-2000). The frequency of high-level resistance to one or more drugs increased from 3.4 percent during 1995-1998 to 12.4 percent during 1999-2000, and the frequency of multi-drug resistance increased from 1.1 percent to 6.2 percent. Among subjects with multi-drug resistance, none identified before 1999 had had resistance for one or more drugs in all three antiretroviral classes, whereas 75 percent of subjects with multi-drug resistance identified in 1999 or 2000 had high-level resistance to all three classes.

Among subjects infected with drug-resistant virus, the time to viral suppression after initiating antiretroviral therapy was longer, and the time to virologic failure was shorter.

Researchers concluded that the proportion of new HIV infections that involve drug-resistant virus is increasing in North America. Initial antiretroviral therapy is more likely to fail in patients who are infected with drug-resistant virus. Testing for resistance to drugs before therapy begins, they write, is now indicated even for recently infected patients.

Editor's Note: from the New England Journal of Medicine