- Clinical science
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.
- Pathogen: P. jirovecii (former P. carinii): ubiquitous, yeast-like fungus previously classified as a protozoan
- Route of transmission: airborne
- Risk factors
A definitive diagnosis of PCP is not always possible. The following criteria should lead to a presumptive diagnosis of PCP:
- History and clinical examination
- Oxygen saturation
- CD4 count
- Beta-D-glucan level
- Chest x-ray (if CXR is inconclusive, a CT scan should be performed)
The diagnosis should generally be confirmed via microscopic identification of P. jirovecii from respiratory secretions.
- Chest auscultation
- Pulse oximetry: oxygen saturation < 90 % at rest (worsens with exertion)
- CD4 count: typically < 200/μL
- Laboratory measures
- ↑ Beta‑D‑glucan levels
- Confirmatory test: microscopic identification of P. jirovecii
- Typically symmetrical, diffuse interstitial infiltrates extending from the perihilar region
- May sometimes be normal
- 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
- Treatment of choice: high‑dose TMP/SMX for up to 3 weeks
- Glucocorticoids: add in the case of severerespiratory insufficiency (either PaO2 < 70 mmHg or arterial‑alveolar oxygen gradient ≥ 35 mmHg)
- Alternatives if allergic to TMP/SMX or treatment of choice is ineffective
If a patient with suspected PCP is acutely ill then empiric treatment should be started without delay.
- PCP was formerly the most common cause of death in HIV‑positive patients during the early years of the HIV epidemic.
- The introduction of 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).