Pneumocystis jirovecii Pneumonia By Sanjay Sethi, MD, University at Buffalo, Jacobs School of Medicine and Biomedical Sciences Reviewed / Revised Sep 2022 View Patient Education Diagnosis Prognosis Treatment Prevention Key Points Topic Resources A-a Gradient Pneumocystis Pneumonia Pneumocystis jirovecii is a common cause of pneumonia in immunosuppressed patients, especially in those infected with human immunodeficiency virus (HIV) and in those receiving systemic corticosteroids.