- Pneumocystis jirovecii pneumonia (PJP) is an AIDS-defining illness because it typically occurs in individuals with severe immunosuppression, particularly those with CD4 counts below 200 cells/µL.
- It signals advanced HIV infection and mandates initiation of antiretroviral therapy.
- Unlike candidiasis of the esophagus or tuberculous lymphadenitis, PJP is specifically listed as an indicator of AIDS by the CDC.
- Herpes labialis is common in the general population and not considered AIDS-defining.

Reference: Harrison’s Principles of Internal Medicine, 20th Edition, Volume 2, Infectious Diseases Chapter