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Pneumocystis jirovecii pneumonia
See also in: Pulmonary
Other Resources UpToDate PubMed

Pneumocystis jirovecii pneumonia

See also in: Pulmonary
Contributors: Neil Mendoza MD, Paritosh Prasad MD, Susan Voci MD, Sumanth Rajagopal MD, William Bonnez MD
Other Resources UpToDate PubMed


Pneumocystis jirovecii, formerly known as Pneumocystis carinii, is the causative agent of Pneumocystis pneumonia (PCP), a disease almost exclusively seen in patients with a compromised immune system (eg, sarcoidosis). Both cell-mediated and humoral immunity are important in control of this infection.

The distribution of the organism is worldwide, and most healthy children are exposed to it within the first 3 years of life, likely due to the inhalation of airborne spores. Some people exposed to P. jirovecii may remain colonized.

Disease manifestations are seen in the setting of immunosuppression.  

Outbreaks of PCP among men who have sex with men heralded the onset of the human immunodeficiency virus (HIV) epidemic. PCP is an AIDS-defining illness and is typically seen in patients infected with HIV with a CD4 cell count of <200/mm3. With improvements in antiretroviral therapy and routine prophylaxis against P. jirovecii in patients infected with HIV and low CD4 cell count, the incidence of infection in this population has decreased, although it remains an important pathogen.

Patients with certain primary immunodeficiencies, including those with severe combined immunodeficiency, are at risk for PCP. Other patients are also at particular risk for PCP due to therapeutic immunosuppression. These include solid organ and autologous and allogenic stem cell transplant recipients. Hospital outbreaks of PCP on solid organ transplantation units have been reported. Patients taking high-dose glucocorticoids (generally considered 20 mg/day for 4 weeks) or other immunosuppressive agents (including tumor necrosis factor-alpha inhibitors) for connective tissue disease, inflammatory bowel disease, or dermatologic conditions are also at increased risk for PCP. Patients undergoing therapy for leukemia or who are receiving T cell-depleting agents or rituximab for other malignancies are also at risk for PCP.

Typical onset in patients with HIV is insidious with a fever, dry cough, and progressive shortness of breath with exertion. There may be associated chest pain. Hemoptysis is not typical. Symptoms may progress for weeks or months before patients seek medical care.

The symptoms are typically more acute in onset and more severe in non-HIV-infected patients. These patients may present with respiratory failure.

Physical examination usually reveals fever, tachycardia, and tachypnea. Breath sounds are often normal, but in up to one-third of adults, rales are present. Impaired oxygenation is a common finding, particularly with ambulation, with varying degrees of hypoxemia and elevated alveolar-arterial (A-a) oxygen gradient.


B59 – Pneumocystosis

79909001 – Pneumocystis carinii

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

Bacterial pneumonia – particularly in the presence of consolidations
  • Streptococcus pneumoniae pneumonia
  • For patients with recent health care exposure, consider resistant gram-positive and gram-negative organisms.
  • Haemophilus influenzae pneumonia species
  • Pulmonary nocardiosis species
  • Legionellosis species
Viral pneumonia – because of the diffuse interstitial pattern
  • Respiratory viruses, including Influenza, Respiratory syncytial virus infection, Parainfluenza virus infection, and Human metapneumovirus infection
  • Varicella pneumonia
  • Herpes simplex virus pneumonia
  • Cytomegalovirus infection
Fungal pneumonia – because of the immunosuppressed status of the patient
  • Cryptococcosis
  • Aspergillosis or other hyaline mold infections (including Scedosporium species or Fusarium species)
  • Mucormycosis
  • Coccidioidomycosis
  • Histoplasmosis
Tuberculosis – especially with the presence of cavities and calcifications

Noninfectious causes – particularly in the presence of nodules
  • Lung cancer
  • Metastatic disease
  • Post-transplant lymphoproliferative disorder

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Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

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Last Updated:08/06/2023
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Pneumocystis jirovecii pneumonia
See also in: Pulmonary
A medical illustration showing key findings of Pneumocystis jirovecii pneumonia : Fever, Dyspnea, Dry cough, HR increased, RR increased
Imaging Studies image of Pneumocystis jirovecii pneumonia - imageId=2956223. Click to open in gallery.  caption: 'Frontal chest x-ray with diffuse, bilateral ground glass opacities with progression to air space consolidation, worse in the lower lobes.'
Frontal chest x-ray with diffuse, bilateral ground glass opacities with progression to air space consolidation, worse in the lower lobes.
Copyright © 2024 VisualDx®. All rights reserved.