Pneumocystis jirovecii - Pneumocystis Pneumonia

Pneumocystis jirovecii is a fungal organism that causes pneumonia predominantly in immunocompromised patients. PCR is the preferred testing method for immunocompromised patients who do not have HIV.

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 (PCP) diagnosis and testing (CDC)
  • Polymerase chain reaction (PCR) – more sensitive than direct fluorescent antibody (DFA) staining
    • Preferred test for immunocompromised patients who do not have HIV – microscopy staining of fluids’ yield is low in these patients
    • Specimens include bronchoalveolar lavage (BAL), sputum, nasopharyngeal wash
  • DFA staining using monoclonal antibodies on induced sputum or BAL
  • Grocott-Gomori methenamine-silver stain or Giemsa stain on lung tissue specimen
  • Culture – cannot be easily cultured
  • Cytopathologic examination of Pap-stained BAL fluid
  • (1,3)-beta-D-glucan assay
    • Up to 30% false-positive rate
    • Not as well studied in P. jirovecii as other fungi

Histology

Immunohistochemistry – P. jirovecii stain

Imaging Studies

  • Chest x-ray
    • Bilateral symmetrical ground-glass opacities
    • 10-25% are normal
  • High resolution computed tomography (CT) – ground-glass opacities

Differential Diagnosis

Background

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
    • Autoimmune disease on multiple drug therapies
    • Primary immunodeficiencies
  • AIDS (CD4+ <200 cells/µL)
  • Organ transplantation
    • Most transplant patients receive Pneumocystis pneumonia (PCP) prophylaxis
    • Heart/lung transplant patients infected with cytomegalovirus (CMV)
    • Solid organ more common

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

ARUP Laboratory Tests

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

Rapid identification of P. jirovecii

Sensitivity dependent on patient population and specimen type

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

Reflex: if DFA is negative, PCR is added

Use for rapid identification of P. jirovecii

Molecular testing is generally preferred; refer to PCR or DFA with reflex to PCR

Sensitivity dependent on patient population and specimen type

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

Aid in histologic diagnosis of P. jirovecii

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

Aid in diagnosis of invasive/disseminated fungal infections (eg, P. jirovecii, Aspergillus, or Candida)

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

Does not detect Zygomycetes (eg, AbsidiaMucorRhizopus)

Yeast phase of Blastomyces dermatitidis may not be detected

Detect respiratory pathogens in patients with pneumonia

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References

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