• Clinical science

Pneumocystis pneumonia


Pneumocystis jirovecii pneumonia (PCP), previously known as Pneumocystis carinii pneumonia, is an opportunistic fungal lung infection occurring almost exclusively in immunocompromised individuals. In 50% of cases, PCP is the first manifestation of AIDS (acquired immune deficiency syndrome), but it may be caused by other immunodeficiency disorders. PCP should be suspected in patients with a history of progressive dyspnea and a dry cough with resistance to standard antibiotic treatment. Signs that support this diagnosis include a CD4 count < 200/μL, an increased beta-D-glucan level, and diffuse bilateral infiltrates on chest x-ray. Management of PCP includes high-dose trimethoprim/sulfamethoxazole (TMP/SMX), treatment of the underlying immunodeficiency disorder, and steroids in the case of severe respiratory insufficiency.





Clinical features

  • Usually asymptomatic
  • Symptoms typically have a gradual onset (days to weeks) and include:
  • May progress to fulminant respiratory failure



A definitive diagnosis of PCP is not always possible. The following criteria should lead to a presumptive diagnosis of PCP:

The diagnosis should generally be confirmed via microscopic identification of P. jirovecii from respiratory secretions.

Clinical examination

PCP is often misdiagnosed as atypical pneumonia or bronchitis because of the persistent cough and similar auscultatory findings.

Laboratory tests

  • CD4 count: typically < 200/μL
  • Laboratory measures
    • Beta‑D‑glucan levels
  • Confirmatory test: microscopic identification of P. jirovecii
    • Specimen from
      • Bronchoalveolar lavage
      • Induced sputum
      • Lung tissue biopsy
    • Staining: enables visualization of disc-shaped P. jirovecii cysts with central spores
      • Methenamine silver staining, Wright stain, or Diff-Quik stain
      • Immunofluorescence


  • Chest x‑ray
    • Typically symmetrical, diffuse interstitial infiltrates extending from the perihilar region
    • May sometimes be normal
  • High-resolution CT
    • Indicated if PCP is still suspected in a patient with a normal CXR
    • High sensitivity for PCP (a negative scan thus suggests the diagnosis of PCP is unlikely)
    • Typical features
      • Ground-glass attenuation: symmetrical diffuse, interstitial infiltrates
      • Pneumatoceles: cystic air-filled spaces within the lung tissue



Acute infection

If a patient with suspected PCP is acutely ill then empiric treatment should be started without delay.

PCP prophylaxis

  • Indication
    • Primary prophylaxis: CD4‑cell count < 200/μl (e.g., AIDS, bone marrow suppression due to cytotoxic therapy, or primary immunosuppressive disorders)
    • Secondary prophylaxis: to prevent recurrence in patients with AIDS or other immunocompromising conditions
  • Implementation



We list the most important complications. The selection is not exhaustive.


  • PCP was formerly the most common cause of death in HIV‑positive patients during the early years of the HIV epidemic.
    • The introduction of HAART (highly active antiretroviral therapy) and TMP/SMX prophylaxis in patients with a CD4 count < 200/μl has significantly improved the long-term outcome of the disease.
    • Despite adequate prophylaxis, PCP infection may lead to death in patients presenting with severe symptoms (e.g., respiratory failure).