Pneumocystis jirovecii

Diagnosis

Indications for Testing

  • Fever, shortness of breath, and cough in immunocompromised patients – particularly those at risk or positive for HIV

Laboratory Testing

  • Pneumocystis pneumonia diagnosis and testing (CDC)
  • Direct fluorescent antibody (DFA) staining using monoclonal antibodies on induced sputum or bronchoalveolar lavage (BAL)
  • Grocott-Gomori methenamine-silver stain or Giemsa stain on lung tissue specimen
  • PCR – more sensitive than DFA staining
    • Preferred test for immunocompromised patients who do not have HIV
    • Specimens include BAL, sputum, nasopharyngeal wash
  • Culture – cannot be easily cultured
  • Cytopathologic examination of Pap-stained BAL fluid
  • (1,3)-beta-D glucan assay – 30% false-positive rate

Histology

  • Immunohistochemistry – P. jirovecii stain

Imaging Studies

  • Chest x-ray – bilateral symmetrical ground-glass opacities
    • 10-25% are normal
  • CT (high-resolution) – ground-glass opacities

Differential Diagnosis

Clinical Background

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

Epidemiology

  • Incidence
    • In AIDS patients – <1/100
    • In solid organ transplant patients not taking prophylactic antibiotics – 5-10/100
  • Sex – M:F equal (except in HIV-positive individuals, where M>F)
  • Transmission – airborne droplets

Organism

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

Risk Factors

  • Immunocompromised status – particularly solid organ transplant patients
  • AIDS (CD4+ <200 cells/µL)
  • Heart/lung transplant patients infected with cytomegalovirus (CMV)

Clinical Presentation

  • Subacute- to acute-onset pneumonia – non-HIV immunocompromised patients more likely to have acute presentation
  • Dyspnea, tachypnea, tachycardia, cyanosis (hypoxemia), nonproductive cough, fever
  • Coinfection with CMV may occur
  • Complications
    • Acute respiratory failure
    • Pneumothorax/pneumomediastinum
    • Dissemination disease – almost exclusively in patients with HIV
      • Most common in lymph nodes, spleen, kidney, liver, thyroid, bone marrow

Indications for Laboratory Testing

  • 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
Test Name and Number Recommended Use Limitations Follow Up
Pneumocystis jirovecii by PCR 2006254
Method: Qualitative Polymerase Chain Reaction

Detect P. jirovecii; preferred test for immunocompromised patients who do not have HIV

More sensitive than DFA

   
Pneumocystis jirovecii DFA with Reflex to Pneumocystis jirovecii by PCR 2009226
Method: Direct Fluorescent Antibody Stain/Qualitative Polymerase Chain Reaction

Rapid identification of P. jirovecii

Reflex – if DFA is negative, PCR is added

Sensitivity dependent on patient population and specimen type

A negative result does not exclude the possibility of infection; false-negative results may occur due to sampling errors or a low number of organisms in the specimen

 
Pneumocystis jirovecii DFA 0060052
Method: Direct Fluorescent Antibody Stain

Rapid identification of P. jirovecii

Sensitivity dependent on patient population and specimen type

A negative result does not exclude the possibility of infection; false-negative results may occur due to sampling errors or a low number of organisms in the specimen

 
(1,3)-Beta-D-Glucan (Fungitell) 2002434
Method: Semi-Quantitative Colorimetry

Detect P. jirovecii

30% false-positive rate

Does not detect fungal species that produce very low levels of (1-3) beta-D-glucan (eg, Cryptococcus)

Does not detect Zygomycetes (eg, Absidia, Mucor, Rhizopus)

 
Pneumocystis jiroveci by Immunohistochemistry 2004103
Method: Immunohistochemistry

Aid in histologic diagnosis of P. jirovecii

Stained and returned to client pathologist for interpretation; consultation available if needed