Pneumocystis jirovecii pneumonia

Pneumocystis jirovecii pneumonia

Infection: Pneumocystis jirovecii pneumonia (PJP), previously Pneumocystis carinii (PCP)

Brief description:
  • Fungal infection that can affect the lungs of immunocompromised people.
  • Higher doses of corticosteroids or other defects in cell-mediated immunity are the main risk factors e.g. advanced HIV (AIDS), haematological cancers, chemotherapy, organ transplantation.
  • A hallmark feature is hypoxia, which may initially only be present with exertion e.g. walking.
Did you know?
  • PJP usually presents with fever, cough and breathlessness that is relatively gradual in onset.
  • Asymptomatic colonisation with P.jirovecii is relatively common, this affects test interpretation.
Who should I test?
  • Test for PJP in people with immunocompromise who present with evidence of respiratory tract infection, especially if treatment for more common pathogens has failed.
  • If the patient is not hypoxic at rest or on walking/exertion then PJP is most unlikely, and other diagnoses should be considered in the first instance.
Test of choice:

Request Pneumocystis PCR

  • PCR of sputum/bronchial washings/other lower respiratory tract sample
  • Excellent sensitivity: a negative result makes the diagnosis very unlikely
  • Moderate specificity: colonisation is relatively common, so detection does not always equate to disease, especially if detected at low levels. 
Tests to avoid/specialist tests:
  • Immunofluorescence/microscopy
    • This has previously been the test of choice, however currently available methods have poor sensitivity or other methodological issues, so PCR is favoured.
Other considerations:
  • In our laboratory PJP is also included in the ‘respiratory multiplex PCR’, which is usually performed on a nasopharyngeal swab (NPS) targeting viral pathogens.
  • The clinical significance of detecting PJP on an upper respiratory tract sample is not entirely clear, however there is evidence to suggest that it is predictive of detection in concurrently collected lower respiratory tract samples.
  • In patients with risk factors and a clinically compatible illness it should therefore usually prompt consideration of further imaging and/or treatment.