pneumocystosis

Pneumocystis pneumonia, also known as pneumocystosis, is an infection caused by Pneumocystis jirovecii. The organism is an airborne, opportunistic fungus-like microbe that commonly colonizes the respiratory tract without causing illness; disease occurs when cell-mediated immunity is compromised. It is a major opportunistic infection in people with advanced HIV/AIDS and in other immunosuppressed patients, such as organ transplant recipients, cancer patients on chemotherapy, and those taking high-dose corticosteroids or other immunosuppressive therapies.

Transmission occurs via inhalation of airborne cysts or trophic forms from an infected person or carrier. Most infections are asymptomatic, but in at-risk individuals the organism proliferates in the alveoli, leading to inflammation and impaired gas exchange. Clinical presentation is typically subacute and may include progressive dyspnea, nonproductive cough, fever, and fatigue. Chest examination can be subtle, while chest imaging usually reveals bilateral diffuse interstitial or alveolar infiltrates; high-resolution CT frequently shows ground-glass opacities.

Diagnosis relies on detection of Pneumocystis jirovecii in respiratory specimens, obtained by induced sputum or bronchoalveolar lavage, using staining methods or immunofluorescence. Polymerase chain reaction (PCR) assays and measurements of serum beta-D-glucan can support the diagnosis but are not definitive alone. Radiographic findings and clinical context are important, particularly in non-HIV immunocompromised patients.

Treatment is first-line with trimethoprim-sulfamethoxazole for about 21 days. Adjunctive corticosteroids are recommended in moderate to severe disease with hypoxemia. Alternatives for those with sulfamethoxazole intolerance include pentamidine, atovaquone, or clindamycin with primaquine.

Prophylaxis is advised for high-risk groups, such as HIV patients with CD4 counts below 200 cells/µL, using daily or thrice-weekly trimethoprim-sulfamethoxazole, with alternatives like dapsone or atovaquone.