Pneumocystis jiroveci

Pneumocystis is a fungal organism that causes pneumonia predominantly in immunocompromised patients.

Epidemiology

• Incidence
  • In AIDS patients, <1/100 person years
  • In solid organ transplant patients – 5-10% prevalence in patients not taking prophylactic antibiotics
• Sex – in AIDS patients, M>F
• Transmission – airborne, as primary infection

Organism

• Classified as a fungus because RNA is homologous to fungal RNA
• Four morphological forms – trophozoites, cysts, precysts, sporozoites
• Cyst is diagnostic form and stains with Giemsa and methenamine silver stains
• Formerly known as Pneumocystis carinii, sp. hominis

Risk Factors

• Immunocompromised patient (particularly solid organ transplant patients)
• AIDS (CD4+  <200 cells/µL)

Clinical Presentation

• Subacute to acute onset pneumonia
• Dyspnea, tachypnea, cyanosis, nonproductive cough, fever
  • Hypoxemia
• Coinfection with cytomegalovirus (CMV) not uncommon
  • High risk for heart-lung transplant patients

Treatment

• Antibiotics
• Glucocorticoids – appear to accelerate recovery
  • Most studied in AIDS patients

Prevention

• Prophylactic use of oral trimethoprim-sulfamethoxazole or inhaled pentamidine significantly reduces the disease rate in at-risk populations

Human Immunodeficiency Virus - HIV  

Diagnosis

• Laboratory testing
  • Direct immunofluorescence staining using monoclonal antibodies on induced sputum or bronchoalveolar lavage (BAL)
    • May also perform Grocott’s methenamine silver nitrate stain and/or Giemsa stain on lung tissue biopsies
  • Cytopathologic examination of Pap-stained bronchoalveolar lavage fluid
• Imaging studies
  • Chest X-ray – bilateral symmetric ground glass opacities
  • 10% are normal
  • CT (high resolution) – ground glass opacities

Indications for Ordering

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory