human immunodeficiency virus infection

an epidemic, transmissible retroviral disease due to infection with human immunodeficiency virus (HIV), which attacks the subset of T lymphocytes known as the CD4 cells. The primary method of transmission is transfer from one person to another of bodily fluids that contain the virus, most commonly semen during sexual intercourse or blood or blood products during transfusions or intravenous injection with a contaminated needle. In its most severe manifestation, meeting specific clinical criteria, it is classified as AIDS (acquired immunodeficiency syndrome; see under syndrome).