• 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

  • Symptoms typically have a gradual onset (days to weeks) and include:
    • Low-grade fever and malaise
    • Dyspnea and non-productive cough
    • Fatigue, weight loss, chills
  • May progress to fulminant respiratory failure
  • Can be asymptomatic



If PCP is suspected; based on the history and clinical examination, oxygen saturation, the CD4+ count, the beta-D-glucan level should be measured and a CXR conducted; . If the CXR is inconclusive, a high-resolution CT scan can be obtained; . The diagnosis should generally be confirmed via microscopic identification of P. jirovecii from respiratory secretions.

Clinical examination

  • Chest auscultation
    • Bilateral crackles and rhonchi
    • Unremarkable auscultatory findings are possible in the early stages of disease.
  • Pulse oximetry: oxygen saturation < 90 % at rest (worsens with exertion)

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
  • ↑ Beta‑D‑glucan
  • Confirmatory test: microscopic identification of P. jirovecii in specimen obtained via bronchoalveolar lavage or induced sputum, with methenamine silver staining and immunofluorescence
    • Staining enables visualization of disc-shaped P. jirovecii cysts with central spores


  • 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



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 below 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).