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:
Patients with HIV infection and CD4+ T cell counts < 200/microL
Organ transplant recipients
Patients with hematologic cancers
Patients taking corticosteroids or other immunosuppressive drugs
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.
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).
If done, pulmonary function tests show altered diffusing capacity (although this is rarely done as a diagnostic test).
Serum beta-D glucan assays are nonspecific but can support the diagnosis.
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. 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.
Treatment is with trimethoprim/sulfamethoxazole (TMP/SMX) 4 to 5 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
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.
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 80/400 mg orally once a day; if this regimen is not tolerated, dapsone 100 mg orally once 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.
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.