Epidemiological aspects of transmitted HIV drug resistance.

Transmitted human immunodeficiency virus (HIV) resistance to antiretrovirals (i.e. resistance in antiretroviral naive patients) emerged during the 1990s as a potentially relevant public health problem. HIV variants resistant to all classes of approved antiretroviral agents have been identified in significant proportions antiretroviral naive patients, and this phenomenon appears as a potential threat to the effectiveness of highly active antiretroviral therapy. Available data from surveys conducted between 1996 and 2001 show the prevalence of drug resistance among newly HIV-infected individuals to range from 3%, to above 20% in North America, and from 5% to 15% in Europe. Increases in prevalence observed during the late 1990s in some studies are not confirmed by most recent data. Transmission of multidrug resistance still appears to be an uncommon occurrence. However, methodological heterogeneity and problems in study design make it difficult to compare results between different surveys and to draw firm conclusions from the results. There is a clear need to improve surveillance systems aimed at identifying patients at the time of primary infection and to standardize laboratory methods for the identification of genetic markers of resistance to be used for epidemiological purposes.