Pneumocystis jiroveci

Indications for Testing

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

Laboratory Testing

PCR – more sensitive than direct fluorescent antibody (DFA) staining; may be particularly useful on non-HIV infected immunocompromised host
- Specimens include bronchoalveolar lavage (BAL), sputum, nasopharyngeal wash, biopsy tissue
- Sensitivity much lower (~80%) if not BAL or tissue
DFA staining using monoclonal antibodies on induced sputum or BAL
- May also perform Grocott’s methenamine silver nitrate stain or Giemsa stain on lung tissue
- Sensitivity of sputum staining – 70-80%
Culture – cannot be readily cultured
Cytopathologic examination of Pap-stained BAL fluid
(1,3)-beta-D glucan – 30% false-positive rate

Histology

Immunohistochemistry – P. jiroveci stain

Imaging Studies

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

Differential Diagnosis

Infectious
- Bacterial
- Viral
  - Influenza
  - Severe acute respiratory syndrome
  - Respiratory syncytial virus
  - Cytomegalovirus
  - Parainfluenza
  - Adenovirus
- Fungal
  - Cryptococcus neoformans
  - Histoplasma capsulatum
  - Coccidioides immitis
  - Blastomyces dermatitidis
Non-infectious
- Hypersensitivity pneumonitis
- Acute respiratory distress syndrome
- Idiopathic pulmonary fibrosis

Pneumocystis 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, in AIDS patients
Transmission – airborne droplet

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 stains
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 coinfected with cytomegalovirus (CMV)

Clinical Presentation

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

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

Tests generally appear in the order most useful for common clinical situations

Test name: Pneumocystis jiroveci DFA

ARUP #: 0060052

Methodology: Direct Fluorescent Antibody Stain

Use:

Rapid identification of P. jiroveci

Limitations:

70-80% sensitivity on sputum sample

Test name: Parasites Smear (Giemsa Stain), Blood

ARUP #: 0049025

Methodology: Stain

Use:

Rapid identification of P. jiroveci

Test name: (1,3)-Beta-D-Glucan (Fungitell®)

ARUP #: 2002434

Methodology: Semi-quantitative Colorimetric Assay

Use:

Detect P. jiroveci

Limitations:

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 (ie, Absidia, Mucor, Rhizopus)

Test name: Pneumocystis jiroveci by Immunohistochemistry

ARUP #: 2004103

Methodology: Immunohistochemistry

Use:

Aid in histologic diagnosis of P. jiroveci

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

General

Comprehensive Review: August 2011
Last Update: August 2011

Community-Acquired Pneumonia

Human Immunodeficiency Virus

Influenza Virus

Respiratory Viruses