Pneumonia Caused by Pneumocystis jiroveci (Pneumocystosis)

How to Cite This Chapter: Loeb M, Kuś J, Jankowski M. Pneumonia Caused by Pneumocystis jiroveci (Pneumocystosis). McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. Accessed July 18, 2024.
Last Updated: October 22, 2021
Last Reviewed: October 22, 2021
Chapter Information

Etiology and PathogenesisTop

Pneumonia caused by Pneumocystis jiroveci (previously Pneumocystis carinii) (PCP) develops in patients with impaired cell-mediated immunity (most commonly in patients with AIDS). The incubation period lasts several weeks.

Clinical presentation: The most common manifestations include fever, dry cough, and dyspnea. In HIV-positive patients, the progression of symptoms may be very slow. White blood cell counts are normal, while lactate dehydrogenase levels are elevated. In patients with early disease, chest radiographs may frequently be normal; later they reveal bilateral, symmetric, ground-glass opacities. Carbon monoxide diffusing capacity of the lungs (DLCO) is decreased.


Detection of trophozoites or cysts of Pneumocystis jiroveci in sputum with special stains, such as Giemsa stain or methenamine silver (sensitivity, 60%), induced sputum, or bronchoalveolar lavage (sensitivity, 95%). In rare cases, lung biopsy (transbronchial or surgical) is necessary.


Sulfamethoxazole/trimethoprim (trimethoprim 15-20 mg/kg/d) IV or orally in 3 or 4 divided doses for 3 weeks. In patients with a contraindication to sulfamethoxazole/trimethoprim with severe PCP, use intravenous pentamidine (4 mg/kg once daily IV). For treatment of mild to moderate PCP in patients who are intolerant of sulfamethoxazole/trimethoprim, alternative regimens include clindamycin (600 mg orally administered every 8 hours in combination with oral primaquine 30 mg once daily), oral atovaquone 750 mg bid, trimethoprim (5 mg/kg orally tid) plus dapsone (100 mg orally once daily). In patients with partial pressure of oxygen in arterial blood (PaO2) <70 mm Hg on room air, an alveolar-arterial (A-a) oxygen gradient ≥35 mm Hg, and/or evidence of hypoxemia (eg, room air oxygen saturation <92%), we suggest a glucocorticoid (oral prednisone 40 mg every 12 hours for 5 days followed by 40 mg/d for 6 days and 20 mg/d for the subsequent 10 days).Evidence 1Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). High Quality of Evidence (high confidence that we know true effects of the intervention). Ewald H, Raatz H, Boscacci R, Furrer H, Bucher HC, Briel M. Adjunctive corticosteroids for Pneumocystis jiroveci pneumonia in patients with HIV infection. Cochrane Database Syst Rev. 2015 Apr 2;(4):CD006150. doi: 10.1002/14651858.CD006150.pub2. Review. PubMed PMID: 25835432.


In immunosuppressed patients and patients with HIV infection who have completed treatment, use sulfamethoxazole/trimethoprim (trimethoprim 80-160 mg orally daily or 160 mg orally 3 times/wk).

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