27th June 2023

Pneumocystis jirovecii pneumonia

Pneumocystis jirovecii (previously Pneumocystis carinii (PCP)) is an airborne transmitted unicellular fungus characteristically infecting immunocompromised patients. In HIV, P. jirovecii infection typically indicates a CD4+ T-cell count is <200/μL, whereas it is often asymptomatic in immunocompetent individuals.

P. jirovecii presents with fever, dry cough, recurrent bacterial pneumonia, and dyspnoea, sometimes with oral candidiasis and weight loss. P. jirovecii may be insidious in HIV, with symptoms over weeks prior to presentation. Auscultation may demonstrate crackles but may be normal. Chest radiography and high-resolution CT may demonstrate bilateral pulmonary interstitial infiltrates, ground-glass opacity, and pneumatoceles (cysts). Pneumocystis is not easily cultured, necessitating microscopic staining, polymerase chain reaction (PCR) or loop-mediated isothermal amplification (LAMP) testing. Broncho-alveolar lavage and induced sputum are used, whereas spontaneously produced sputum has lower sensitivity. β-D-glucan, which is found in cell walls of Pneumocystis, and some other fungi, can screen for possible Pneumocystis infection but is non-specific.

Management for P. jirovecii usually involves co-trimoxazole for 21 days, however, there is some resistance. Co-trimoxazole is also used in prophylaxis for P. jirovecii in patients with a CD4+ T cell count <200 cells/μL. Lower CD4+ T-cells indicate a poorer prognosis. Mortality is ~10% in hospitalised patients.