Merck Manual

Please confirm that you are a health care professional

honeypot link

Pneumocystis jirovecii Pneumonia


Sanjay Sethi

, MD, University at Buffalo, Jacobs School of Medicine and Biomedical Sciences

Reviewed/Revised Sep 2022
Topic Resources

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. 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 plus trimethoprim, clindamycin/primaquine, atovaquone, or pentamidine. Patients with PaO2 < 70 mm Hg receive systemic corticosteroids. Prognosis is generally good with timely treatment.

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

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.

Diagnosis of Pneumocystis jirovecii Pneumonia

  • Chest x-ray

  • Pulse oximetry

  • Histopathologic confirmation

To diagnose Pneumocystis jirovecii pneumonia, 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, arterial blood gas (ABG) measurements are often obtained to show severity of hypoxemia (including an increase in the alveolar-arterial oxygen gradient).

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.

Serum beta-D glucan assays are nonspecific but can support the diagnosis.

Histopathologic demonstration of Pneumocystis jirovecii is needed for confirmation of the diagnosis. Methenamine silver, Giemsa, Wright-Giemsa, modified Grocott, Weigert-Gram, or monoclonal antibody stain is used. Polymerase chain reaction (PCR)-based detection can add to the diagnostic yield. 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.

Prognosis for Pneumocystis jirovecii Pneumonia

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

Treatment of Pneumocystis jirovecii Pneumonia

  • Trimethoprim/sulfamethoxazole

  • Corticosteroids if PaO2 < 70 mm Hg

Treatment is with trimethoprim/sulfamethoxazole (TMP/SMX) 15 to 20 mg/kg IV or orally 3 times a day 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 acquired immunodeficiency syndrome (AIDS) and include rash, neutropenia, hepatitis, and fever.

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

  • Pentamidine 4 mg/kg IV once a day

  • Atovaquone 750 mg orally 2 times a day

  • Trimethoprim 5 mg/kg orally 3times a day with dapsone 100 mg orally once a day

  • Clindamycin 900 mg IV every 8 hours, 600 mg IV every 6 hours, 600 mg orally 3 times a day, or 450 mg orally 4 times a day, plus primaquine base 30 mg orally once a day

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 orally twice a day (or its equivalent) for the first 5 days, 40 mg orally once a day for the next 5 days (or 20 mg twice a day), and then 20 mg orally once a day for the duration of treatment.

Prevention of Pneumocystis jirovecii Pneumonia

HIV-infected patients who have had P. jirovecii pneumonia or who have a CD4+ T cell count < 200/microL should receive prophylaxis with TMP/SMX 160/800 mg orally once a day or TMP/SMX 80/400 mg orally once a day; if this regimen is not tolerated, dapsone 100 mg orally once a day (or 50 mg orally twice a day) or aerosolized pentamidine 300 mg once a month can be used. These prophylactic regimens are also indicated for many non–HIV-infected patients at risk of P. jirovecii pneumonia.

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 samples.

  • Treat patients with trimethoprim/sulfamethoxazole, adding a corticosteroid if PaO2 is < 70 mm Hg.

Drugs Mentioned In This Article

Drug Name Select Trade
Primsol, Proloprim, TRIMPEX
Cleocin, Cleocin Ovules, Cleocin Pediatric, Cleocin T, CLIN, Clindacin ETZ, Clindacin-P, Clinda-Derm , Clindagel, ClindaMax, ClindaReach, Clindesse, Clindets, Evoclin, PledgaClin, XACIATO
NebuPent, Pentam
Hiprex, Mandelamine, Urex
Deltasone, Predone, RAYOS, Sterapred, Sterapred DS
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
quiz link

Test your knowledge

Take a Quiz!