Pneumocystis jirovecii pneumonia is a fungal infection of the lungs. The disease used to be called Pneumocystis carinii or PCP pneumonia.

Pneumocystis pneumonia; Pneumocystis; PCP; Pneumocystis carinii; PJP pneumonia

This type of pneumonia is caused by the fungus Pneumocystis jirovecii. This fungus is common in the environment and rarely causes illness in healthy people.

However, it can cause a lung infection in people with a weakened immune system due to:

• Cancer
• Long-term use of corticosteroids or other medicines that weaken the immune system
• HIV/AIDS
• Organ or bone marrow transplantation

Pneumocystis jirovecii was a rare infection before the AIDS epidemic. Before the use of preventive antibiotics for the condition, most people in the United States with advanced AIDS developed this infection.

Pneumocystis pneumonia in people with AIDS usually develops slowly over days to weeks or even months, and is less severe. People with pneumocystis pneumonia who do not have AIDS usually get sick faster and are more severely ill.

Symptoms include:

• Cough, often mild and dry
• Fever
• Rapid breathing
• Shortness of breath, especially with activity (exertion)

Anti-infection medicines can be given by mouth (orally) or through a vein (intravenously), depending on how severe the illness is.

People with low oxygen levels and moderate to severe disease are often prescribed corticosteroids as well.

Pneumocystis pneumonia can be life threatening. It can cause respiratory failure that can lead to death. People with this condition need early and effective treatment. For moderate to severe pneumocystis pneumonia in people with HIV/AIDS, the short term use of corticosteroids has decreased the incidence of death.

Complications that may result include:

• Pleural effusion (extremely rare)
• Pneumothorax (collapsed lung)
• Respiratory failure (may require breathing support)

If you have a weakened immune system due to AIDS, cancer, transplantation, or corticosteroid use, contact your provider if you develop a cough, fever, or shortness of breath.

Preventive therapy is recommended for:

• People with HIV/AIDS who have CD4 counts below 200 cells/microliter or 200 cells/cubic millimeter
• Bone marrow transplant recipients
• Organ transplant recipients
• People who take long-term, high-dose corticosteroids
• People who have had previous episodes of this infection
• People who take long-term immunomodulatory medicines

Published Date: December 13, 2025
Published By: Jatin M. Vyas, MD, PhD, Roy and Diana Vagelos Professor in Medicine, Columbia University Vagelos College of Physicians and Surgeons, Division of Infectious Diseases, Department of Medicine, New York, NY. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

Kovacs JA. Pneumocystis pneumonia. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 313.

Smulian AG, Miller-Handley H, Miller RF. Pneumocystis species. In: Blaser MJ, Cohen JI, Holland SM, et al, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 10th ed. Philadelphia, PA: Elsevier; 2026:chap 275.