Open wound in AIDS. This wound developed after drainage of septic arthritis of the knee. Septic arthritis is a bacterial infection of the joints. It is rare in healthy individuals, especially in the young (this patient is 23 years old). AIDS (acquired immune deficiency syndrome) is a contagious disease caused by the human immunodeficiency virus (HIV). It causes weakening of the immune system, which allows opportunistic infections to take hold, and makes normally minor infections life-threatening. This patient is from Africa, where a lack of access to drugs and information makes AIDS a major public health concern.