Pneumocystosis (Pneumocystis jirovecii Pneumonia)

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

Diagnosis

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

Treatment

Medications

• 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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