A new study led by the Harvard Center for Risk Analysis, published in the Annals of Internal Medicine in March 2001, finds that testing people with HIV to determine whether they have a drug-resistant strain of the virus is a cost-effective use of resources in the battle against HIV. In fact, the study finds that investing in this genetic resistance testing is approximately as cost-effective as the money spent on the drug therapy itself. Despite significant gains in treating people with HIV, antiretroviral drug therapy initially fails in nearly half of those patients. A common reason is that the virus develops resistance to some of the drug being used. Genetic testing to identify strains of the virus that are drug resistant can help clinicians adjust the “AIDS cocktail” mix of drugs so therapy is more effective.