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Key Features

Essentials of Diagnosis

  • Fever, dyspnea, dry cough, hypoxia with exertion

  • Often only slight lung physical findings

  • Chest radiograph: diffuse interstitial disease or normal

  • Detection of P jirovecii in sputum, bronchoalveolar lavage fluid, or lung tissue, PCR in bronchoalveolar lavage; (1,3)-β-D-glucan in blood

General Considerations

  • P jirovecii affects humans worldwide

  • Based on serology, asymptomatic infections occur at a young age in most persons

  • Overt infection is an acute interstitial plasma cell pneumonia that occurs with high frequency among two groups

    • Premature infants on hospital wards in underdeveloped parts of the world (epidemics of primary infection)

    • Older children and adults with 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

      • Treatment with immunosuppressive medications, such as corticosteroids or cytotoxic agents

  • Evidence suggests airborne transmission

  • Pneumocystis pneumonia occurs in up to 80% of AIDS patients not receiving prophylaxis, usually at CD4 cell counts < 200/mcL

  • In non-AIDS patients taking immunosuppressives, symptoms often begin when corticosteroids are tapered or discontinued

Clinical Findings

Symptoms and Signs

  • Subacute onset characterized by dyspnea on exertion and nonproductive cough

  • Patients with AIDS usually have other evidence of HIV-associated disease, including

    • Fever

    • Fatigue

    • Weight loss

  • Bibasilar crackles present in some patients

  • Findings may be slight and disproportionate to the degree of illness and radiologic findings

  • Spontaneous pneumothorax may occur if patient had previous episodes or received aerosolized pentamidine prophylaxis

  • Extrapulmonary disease is reported rarely and usually occurs in individuals who are receiving aerosolized pentamidine prophylaxis


Laboratory Tests

  • Arterial blood gas shows hypoxemia and hypocapnia; peripheral oxygen saturation may be normal at rest but decreases rapidly with exercise

  • Measurement of serum (1,3)-β-D-glucan levels has good sensitivity and specificity

  • Culture not possible

  • Polymerase chain reaction (PCR) of bronchoalveolar lavage (BAL) is overly sensitive

    • Can be positive in colonized, uninfected persons

    • However, quantitative values may help with identifying infected patients

    • Negative PCR from BAL rules out disease

Imaging Studies

  • Chest radiograph

    • Usually shows diffuse interstitial infiltrates, but early in infection, these may be heterogeneous, miliary, or patchy

    • May also show diffuse or focal consolidation, cystic changes, nodules, or cavitation within nodules

    • Pleural effusions not seen

  • Chest radiograph is normal in 5–10%; high-resolution chest CT better able to demonstrate mild disease

  • Upper lobe infiltrates common if patient received aerosolized pentamidine prophylaxis



  • Empiric therapy may be started if disease is suspected clinically

  • In patients with mild to moderately severe disease, continued treatment should be based on a proven diagnosis because of


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