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Pneumocystis jirovecii Pneumonia

by Sanjay Sethi, MD

P. jirovecii is a common cause of pneumonia in immunosuppressed patients (see Pneumonia in Immunocompromised Patients), especially in those infected with HIV and in those receiving systemic corticosteroids. Symptoms include fever, dyspnea, and dry cough. Diagnosis requires demonstration of the organism in an induced sputum specimen or bronchoscopic sample. Treatment is with antibiotics, usually trimethoprim/sulfamethoxazole or dapsone/trimethoprim, clindamycin/primaquine, atovaquone, or pentamidine. Patients with Pao2< 70 mm Hg receive systemic corticosteroids. Prognosis is generally good with timely treatment.

P. jirovecii is a ubiquitous organism transmitted by aerosol route and causes no disease in immunocompetent patients (see Overview of Pneumonia). However, some patients are at risk of developing P. jirovecii pneumonia:

  • Patients with HIV infection and CD4+ counts < 200/μL

  • Organ transplant recipients

  • Patients with hematologic cancers

  • Patients taking corticosteroids

Most patients have fever, dyspnea, and a dry, nonproductive cough that evolves over several weeks (HIV infection) or over several days (other causes of compromised cell-mediated immunity). Dyspnea is common.


  • Chest x-ray

  • Pulse oximetry

  • Histopathologic confirmation

Patients should have chest x-ray and assessment of oxygenation by pulse oximetry.

Chest x-ray characteristically shows diffuse, bilateral perihilar infiltrates, but 20 to 30% of patients have normal x-rays.

Hypoxemia may be present even when chest x-ray shows no infiltrate; this finding can be an important clue to diagnosis. When pulse oximetry is abnormal, ABGs are often obtained to show severity of hypoxemia (including an increase in the alveolar-arterial O2gradient).

Pearls & Pitfalls

  • In immunosuppressed patients who have a dry, nonproductive cough and abnormal chest x-ray or pulse oximetry, pursue further testing for P. jirovecii pneumonia.

If done, pulmonary function tests show altered diffusing capacity (although this is rarely done as a diagnostic test).

Histopathologic demonstration of the organism is needed for confirmation of the diagnosis. Methenamine silver, Giemsa, Wright-Giemsa, modified Grocott, Weigert-Gram, or monoclonal antibody stain is used. Sputum specimens are usually obtained by induced sputum or bronchoscopy. Sensitivity ranges from 30 to 80% for induced sputum and is > 95% for bronchoscopy with bronchoalveolar lavage.


Overall mortality for P. jirovecii pneumonia in hospitalized patients is 15 to 20%. Risk factors for death may include previous history of P. jirovecii pneumonia, older age, and, in HIV-infected patients, CD4+ cell count < 50/μL.


  • Trimethoprim/sulfamethoxazole

  • Corticosteroids if Pao2< 70 mm Hg

Treatment is with trimethoprim/sulfamethoxazole (TMP/SMX) 4 to 5 mg/kg IV or po tid for 14 to 21 days. Treatment can be started before diagnosis is confirmed because P. jirovecii cysts persist in the lungs for weeks. Adverse effects of treatment are more common among patients with AIDS and include rash, neutropenia, hepatitis, and fever.

Alternative regimens, which are also given for 21 days, are

  • Pentamidine 4 mg/kg IV once/day

  • Atovaquone 750 mg po bid

  • Trimethoprim 5 mg/kg po qid with dapsone 100 mg po once/day

  • Clindamycin 300 to 900 mg IV q 6 to 8 h with primaquine base 15 to 30 mg/day po

The major limitation of pentamidine is the high frequency of toxic adverse effects, including acute kidney injury, hypotension, and hypoglycemia. Adjunctive therapy with corticosteroids is recommended for patients with a Pao2< 70 mm Hg. The suggested regimen is prednisone 40 mg po bid (or its equivalent) for the first 5 days, 40 mg po once/day for the next 5 days (or 20 mg bid), and then 20 mg po once/day for the duration of treatment.


HIV-infected patients who have had P. jirovecii pneumonia or who have a CD4+ count < 200/μL should receive prophylaxis with TMP/SMX 80/400 mg once/day; if this regimen is not tolerated, dapsone 100 mg po once/day or aerosolized pentamidine 300 mg once/month can be used. These prophylactic regimens are also probably indicated for non–HIV-infected patients at risk of P. jiroveciipneumonia.

Key Points

  • Consider P. jirovecii pneumonia in patients who are immunosuppressed, even if they have mild respiratory symptoms and even if the chest x-ray is normal.

  • Do histopathologic examination on induced sputum or bronchoscopically obtained sputum.

  • Treat patients with trimethoprim/sulfamethoxazole, adding a corticosteroid if Pao2is < 70 mm Hg.

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