Which is an AIDS-defining illness?

• A. Pneumocystis jirovecii pneumonia
• B. Common cold
• C. Seasonal influenza
• D. Bacterial sinusitis

Answer: (A)

Pneumocystis jirovecii pneumonia is an AIDS-defining illness because its occurrence in someone with HIV signals severe immune suppression and meets the criteria for diagnosing AIDS. AIDS can be diagnosed when the CD4 count drops below 200 cells/µL or when an AIDS-defining condition appears, and Pneumocystis pneumonia is one of the classic infections that define that stage. The other infections listed—common cold, seasonal influenza, and bacterial sinusitis—are common illnesses that can occur at any immune level and do not by themselves indicate progression to AIDS. PCP typically presents with gradual onset of fever, progressive difficulty breathing, and a nonproductive cough, with diffuse bilateral infiltrates on imaging and diagnosis made from respiratory samples.