ESSENTIALS OF DIAGNOSIS
Fever, dyspnea, dry cough, hypoxia.
Often only slight lung physical findings.
Chest radiograph: diffuse interstitial disease or normal.
P jirovecii in sputum, bronchoalveolar lavage fluid, or lung tissue; PCR of bronchoalveolar lavage; (1,3)-beta-D-glucan in blood.
Pneumocystis jirovecii, the Pneumocystis species that affects humans, is distributed worldwide. Although symptomatic P jirovecii disease is rare in the general population, serologic evidence indicates that asymptomatic infections have occurred in most persons by a young age. Accumulating evidence suggests airborne transmission. Following asymptomatic primary infection, latent and presumably inactive organisms are sparsely distributed in the alveoli. De novo infection and reactivation of latent disease likely contribute to the mechanism of acute disease in older children and adults.
The overt infection is an acute interstitial plasma cell pneumonia that occurs with high frequency among two groups: (1) as epidemics of primary infections among premature infants on hospital wards in underdeveloped parts of the world, and (2) as sporadic cases among older children and adults who have an abnormal or altered cellular immunity, either due to an underlying disease process (eg, cancer, malnutrition, stem cell or organ transplantation or, most commonly, AIDS) or due to treatment with immunosuppressive medications, such as corticosteroids or cytotoxic agents.
Pneumocystis pneumonia occurs in up to 80% of AIDS patients not receiving prophylaxis and is a major cause of death. Its incidence increases in direct proportion to the fall in CD4 cells, with most cases occurring at CD4 cell counts less than 200/mcL. In non-AIDS patients receiving immunosuppressive therapy, symptoms frequently begin after corticosteroids have been tapered or discontinued.
Findings are usually limited to the pulmonary parenchyma; extrapulmonary disease is reported rarely and usually occurs in individuals who are receiving aerosolized pentamidine prophylaxis. In the sporadic form of the disease associated with deficient cell-mediated immunity, the onset may be subacute, characterized by dyspnea on exertion and nonproductive cough. Pulmonary physical findings may be slight and disproportionate to the degree of illness and the radiologic findings; many patients have bibasilar crackles. Without treatment, the course is usually one of rapid deterioration and death. Adult patients may present with spontaneous pneumothorax, usually in patients with previous episodes or those receiving aerosolized pentamidine prophylaxis. Patients with AIDS will usually have other evidence of HIV-associated disease, including fever, fatigue, and weight loss, for weeks or months preceding the illness.
Chest radiographs most often show diffuse “interstitial” infiltration, which may be heterogeneous, miliary, or patchy early in infection. There may also be diffuse or focal consolidation, cystic changes, nodules, or cavitation within nodules. Pleural effusions are not seen. About 5–10% of patients with Pneumocystis pneumonia have normal chest films. High-resolution chest CT scans may be quite suggestive of P jirovecii pneumonia, helping distinguish it from other ...