I: Certain infectious and parasitic diseases

B20-B24: Human immunodeficiency virus [HIV] disease

Human immunodeficiency virus (HIV) disease can be seen as a spectrum of conditions, all caused by a virus that attacks the immune system. Primarily transmitted through contact with certain body fluids—like blood, semen, vaginal fluids, and breast milk—it latches onto cells that help protect against disease and infections, harming them in the process. At the beginning, it may cause flu-like symptoms like fever, sore throat, or rash. As the virus progresses, these initial symptoms may disappear, but the disease continues to affect the body. Over time, particularly without treatment, it can lead to severe illnesses as the immune system weakens. People with HIV might get infections that are more frequent, chronic, and severe because the body lacks the defensive tools to fight them off. Eventually, it may develop into acquired immunodeficiency syndrome (AIDS), the most advanced stage of HIV.