Pneumocystis pneumonia

Last updated: September 26, 2023

Summarytoggle arrow icon

Pneumocystis jirovecii pneumonia (PCP), previously known as Pneumocystis carinii pneumonia, is an opportunistic fungal lung infection occurring almost exclusively in immunocompromised individuals. It is an HIV-associated condition but may be caused by other immunodeficiencies, including primary immunodeficiency disorders, immunodeficiency resulting from malignancy, following a solid organ or stem cell transplant, or secondary to the long-term use of immunosuppressants such as high-dose steroids. PCP should be suspected in immunocompromised patients with a history of progressive dyspnea, dry cough, or hypoxia. Other findings that further support the diagnosis include an increase in β-d-Glucan and LDH levels, and diffuse bilateral infiltrates on chest imaging. PCP is confirmed if P. jirovecii is detected on an induced sputum sample, bronchoalveolar lavage, or lung tissue biopsy. Management of PCP includes high-dose trimethoprim/sulfamethoxazole (TMP/SMX), treatment of the underlying immunodeficiency disorder, and, in some cases, adjunctive glucocorticoids. Prophylaxis regimens for PCP should be considered for patients with significant immunosuppression and commonly include the use of long-term, low-dose TMP/SMX.

Definitiontoggle arrow icon

Etiologytoggle arrow icon

Clinical featurestoggle arrow icon

Symptoms of PCP [5][6]

The clinical course of PCP is usually more acute and severe in HIV-negative patients compared to HIV-positive patients. HIV-positive patients often initially have an indolent course with mild exertional symptoms and no fever or cough. [5][6][7]

Clinical examination [5][6]

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

Diagnosticstoggle arrow icon

Consider PCP in patients with respiratory symptoms or unexplained hypoxia and a history of HIV or other causes of impaired humoral immunity (e.g., organ transplantation, immunosuppressive medications, malignancy). See also “Diagnosis of pneumonia.”

Approach [6][8]

Clinical presentation, laboratory studies, and imaging studies are not pathognomonic for PCP. Maintain a broad differential diagnosis and seek a definitive diagnosis of PCP when possible.

Because P. jirovecii cannot be routinely cultured, it requires confirmation via histopathological, cytopathological, or molecular identification of P. jirovecii from respiratory secretions or lung tissue.

Initial studies

Laboratory studies [6]

Imaging studies [6]

  • X-ray chest
    • Order initially for all patients.
    • Findings
      • Diffuse, bilateral, symmetrical, interstitial infiltrates extending from the perihilar region (butterfly pattern)
      • May be normal in the early stages of PCP
  • CT chest without contrast (HRCT may increase diagnostic accuracy)
    • Indicated if PCP is still suspected in a patient with a normal chest x-ray
    • Findings
    • A normal CT effectively rules out the diagnosis.

Patients with PCP rarely present with lung cavitations or pleural effusions on chest x-ray. If these findings are present, consider alternative diagnoses or additional pathology. [6]

Diagnostic confirmation [6]

Spontaneously expectorated sputum should not be used for diagnostic studies because it has poor sensitivity for PCP. Use induced sputum instead. [6]

Treatmenttoggle arrow icon

PCP treatment [5][6][7][11]

  • General considerations
    • If clinical suspicion is high, treatment can be initiated before a definitive diagnosis is established.
    • Treatment recommendations vary depending on the patient's HIV status and PCP disease severity.
  • Disease severity
  • Antibiotic therapy
    • High-dose TMP/SMX is the treatment of choice.
    • A 21-day antibiotic course is recommended for most patients, regardless of the antibiotic regimen. [7]
    • For patients with treatment failure :
      • Consider changing to an alternative antibiotic regimen under the guidance of an infectious disease specialist.
      • Exclude concomitant infections.
Antibiotic therapy for PCP [6]
Preferred Alternative
Mild to moderate PCP
Moderate to severe PCP

TMP/SMX can still be an effective treatment for patients who develop PCP despite TMP/SMX prophylaxis.

The benefit of adjunctive glucocorticoid therapy for PCP in HIV-negative patients is unclear. [12]

PCP prophylaxis [5][6][13][14]

Complicationstoggle arrow icon

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

Prognosistoggle arrow icon

Referencestoggle arrow icon

  1. Stringer JR, Beard CB, Miller RF, Wakefield AE. A New Name for Pneumocystis from Humans and New Perspectives on the Host-Pathogen Relationship. Emerg Infect Dis. 2002; 8 (9): p.891–896.doi: 10.3201/eid0809.020096 . | Open in Read by QxMD
  2. Morris A, Lundgren JD, Masur H, et al. Current epidemiology of Pneumocystis pneumonia. Emerg Infect Dis. 2004; 10 (10): p.1713-1720.doi: 10.3201/eid1010.030985 . | Open in Read by QxMD
  3. Huang L, Crothers KA. HIV-associated Opportunistic Pneumonias. Respirology. 2009; 14 (4): p.474–485..doi: 10.1111/j.1440-1843.2009.01534.x . | Open in Read by QxMD
  4. X-linked Immunodeficiency With Hyper IgM Clinical Presentation. Updated: October 23, 2019. Accessed: March 9, 2020.
  5. Fishman JA, Gans H. Pneumocystis jiroveciin solid organ transplantation: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice. Clin Transplant. 2019; 33 (9).doi: 10.1111/ctr.13587 . | Open in Read by QxMD
  6. Guidelines for the prevention and treatment of opportunistic infections in adults and adolescents with HIV: Recommendations from the Center for Disease Control and Prevention, the National Institutes of Health, and the HIV Medicine Association of the Infectious Disease Society of America.. Updated: March 28, 2019. Accessed: September 3, 2021.
  7. Jameson JL, Fauci AS, Kasper DL, Hauser SL, Longo DL, Loscalzo J. Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2). McGraw-Hill Education / Medical ; 2018
  8. Limper AH, Knox KS, Sarosi GA et al. An official American Thoracic Society statement: treatment of fungal infections in adult pulmonary and critical care patients. Am J Respir Crit Care Med. 2011; 183 (1): p.96-128.doi: 10.1164/rccm.2008-740ST . | Open in Read by QxMD
  9. Salerno D, Mushatt D, Myers L et al. Serum and bal beta-D-glucan for the diagnosis of Pneumocystis pneumonia in HIV positive patients. Respir Med. 2014; 108 (11): p.1688-1695.doi: 10.1016/j.rmed.2014.09.017 . | Open in Read by QxMD
  10. Esteves F, Calé SS, Badura R, et al. Diagnosis of Pneumocystis pneumonia: evaluation of four serologic biomarkers. Clinical Microbiology and Infection. 2014; 21 (4): p.379.e1-379.e10.doi: 10.1016/j.cmi.2014.11.025 . | Open in Read by QxMD
  11. Maschmeyer G, Helweg-Larsen J, Pagano L, Robin C, Cordonnier C, Schellongowski P. ECIL guidelines for treatment of Pneumocystis jirovecii pneumonia in non-HIV-infected haematology patients. J Antimicrob Chemother. 2016; 71 (9): p.2405-2413.doi: 10.1093/jac/dkw158 . | Open in Read by QxMD
  12. Injean P, Eells SJ, Wu H, McElroy I, Gregson AL, McKinnell JA. A Systematic Review and Meta-Analysis of the Data Behind Current Recommendations for Corticosteroids in Non–HIV-Related PCP: Knowing When You Are on Shaky Foundations. Transplantation Direct. 2017; 3 (3): p.e137.doi: 10.1097/txd.0000000000000642 . | Open in Read by QxMD
  13. Park JW, Curtis JR, et al.. Prophylactic effect of trimethoprim-sulfamethoxazole for pneumocystis pneumonia in patients with rheumatic diseases exposed to prolonged high-dose glucocorticoids. Ann Rheum Dis.. 2017.doi: 10.1136/annrheumdis-2017-211796 . | Open in Read by QxMD
  14. Maertens J, Cesaro S, Maschmeyer G, et al. ECIL guidelines for preventing Pneumocystis jirovecii pneumonia in patients with haematological malignancies and stem cell transplant recipients. J Antimicrob Chemother. 2016; 71 (9): p.2397-2404.doi: 10.1093/jac/dkw157 . | Open in Read by QxMD
  15. Quinn M, Fannin JT, Sciasci J, et al. Pentamidine for Prophylaxis against Pneumocystis jirovecii Pneumonia in Pediatric Oncology Patients Receiving Immunosuppressive Chemotherapy. Antimicrobial Agents Chemother (Bethesda). 2018; 62 (8).doi: 10.1128/aac.00173-18 . | Open in Read by QxMD
  16. Awad WB, Asaad A, Al-Yasein N, Najjar R. Effectiveness and tolerability of intravenous pentamidine for Pneumocystis carinii pneumonia prophylaxis in adult hematopoietic stem cell transplant patients: a retrospective study. BMC Infect Dis. 2020; 20 (1).doi: 10.1186/s12879-020-05127-y . | Open in Read by QxMD

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