Acquired immunodeficiency syndrome (AIDS) is the last stage of infection with the human immunodeficiency virus (HIV). AIDS weakens the immune system and increases a person's risk of developing serious illnesses such as certain cancers, opportunistic diseases, and neurological disorders.

HIV is spread through contaminated blood, specifically through sexual contact or shared needles. HIV, especially if it is not treated, can progress to AIDS. Symptoms of AIDS include fatigue, weight loss, diarrhea, fever, night sweats, thrush (infection in the mouth and throat), and swollen lymph nodes of the neck, armpits, and groin.