This is a retrospective observational study which follows on from CNA106030 (a study evaluating whether prospective genetic screening for HLA-B*5701 can reduce the incidence of hypersensitivity reactions to abacavir). This study aims to collect data on approximately 35 subjects who withdrew from CNA106030 when found to be HLA-B*5701 positive. HIV disease management and adverse event data in these subjects, where the risk/benefit ratio of treatment with abacavir may alter subsequent prescribing, will be collected

Inclusion Criteria:

• Subjects who have received notification not to receive abacavir in the CNA106030 study because of a positive HLA-B*5701 screen result, and were subsequently withdrawn from protocol CNA106030.
• Subjects willing and able to understand and provide written informed consent prior to participation in this study.
• French subjects: In France, a subject will be eligible for inclusion in this study only if either affiliated to or a beneficiary of a social security category.

Exclusion criteria:

• Subjects who were not enrolled in the CNA106030 study
• Subjects who are not HLA-B*5701 positive
• Subjects who do not consent to being told their HLA-B*5701 status