Pneumocystis Infections

Pneumocystis pneumonia (PCP), caused by the fungal organism Pneumocystis jirovecii, is a serious and potentially life-threatening lung infection that occurs almost exclusively in people with weakened immune systems. During the early years of the AIDS epidemic, PCP was the AIDS-defining illness for as many as two-thirds of patients in the United States, and it remains the most common serious opportunistic infection in people living with HIV. The landscape of PCP has shifted significantly with the advent of antiretroviral therapy — rates of PCP among hospitalized HIV patients declined from 6.7% in 2002 to 3.5% in 2014 — but the disease has not disappeared. The prevalence of non-HIV immunocompromising conditions among PCP hospitalizations has increased, with malignancy now the most common underlying condition, followed by organ transplantation, autoimmune diseases, and long-term corticosteroid use. Non-HIV patients with PCP face significantly worse outcomes than HIV patients, including higher rates of intubation, longer hospitalizations, and in-hospital mortality of 16% compared to 5% in HIV patients. Prevention through prophylactic trimethoprim-sulfamethoxazole (TMP-SMX) remains highly effective for high-risk populations, and prompt diagnosis and treatment are critical given the rapid progression of disease.