The purpose of this study is to find out the frequency of the I50L substitution among patients experiencing treatment failure on an atazanavir-containing regimen.

Inclusion Criteria:

• Atazanavir - containing antiretroviral regimen

• Confirmed virologic failure defined as either:

  1. HIV RNA by PCR greater than or equal to 1000 copies/mL after achieving a value of <400 copies/mL on at least 2 consecutive measurements or
  2. HIV RNA greater than or equal to 1000 copies/mL after 24 weeks of continuous therapy

• At least 18 years old

Exclusion Criteria:

• Unable to give informed consent
• Prisoners or subjects involuntarily incarcerated for treatment of psychiatric or physical illness

HIV infected patients failing HAART regimen