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Pneumocystis pneumonia
Background
Overview
Definition
PCP is a severe opportunistic fungal infection caused by P. jirovecii, primarily affecting immunocompromised individuals.
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Pathophysiology
The pathophysiology of PCP involves airborne transmission of the fungus, which then invades lung tissue and adheres to type 1 epithelial cells. The attachment of Pneumocystis to the alveolar epithelium promotes the transition of the organism from the trophic to the cyst form, leading to the production of inflammatory mediators, lung injury, and impaired gas exchange.
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Epidemiology
The incidence of PCP is estimated at 2.2-4.5 per 100,000, with more than 80% occurring in patients without HIV. In the US, approximately 10,500 hospitalizations and 400 deaths are reported annually due to PCP.
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Risk factors
Risk factors for PCP include HIV infection with a low CD4+ T-cell count, malignancies, solid organ transplantation, hematologic stem cell transplantation, prolonged use of corticosteroids and other immunosuppressive agents, such as chemotherapy (especially purine analogs), T-cell-depleting agents, TNF-α inhibitors, anti-interleukin 6, anti-CD26, and calcineurin inhibitors.
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Disease course
Clinically, PCP often presents with a progressive nonproductive cough, exertional dyspnea, chest pain, and fever. Patients with HIV may have an indolent course, while patients without HIV usually present with rapidly progressive onset.
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Prognosis and risk of recurrence
The mortality rate of PCP in patients with and without HIV is estimated at 25% and 33-69%, respectively.
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Guidelines
Key sources
The following summarized guidelines for the evaluation and management of Pneumocystis pneumonia are prepared by our editorial team based on guidelines from the U.S. Department of Health and Human Services (DHHS 2025), the British HIV Association (BHIVA 2024), the British Society for Haematology (BSH 2024,2022,2018), the European League Against Rheumatism (EULAR 2024), the European Respiratory Society (ERS/EBMT 2024), the Consensus ...
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Screening and diagnosis
Classification and risk stratification
Severity assessment
As per ECIL 2016 guidelines:
Use the Miller grading system to assess the severity of PCP.
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Do not use conventional grading systems used for community-acquired pneumonia (such as A-DROP, CURB-65, or PSI) for the assessment of PCP severity, as they underestimate the severity of PCP.
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Miller criteria for PCP severity assessment
Symptoms and signs
Dyspnea on exertion with or without cough and sweats
Dyspnea on minimal exertion, occasional dyspnea at rest, fever, cough
Dyspnea at rest, tachypnea at rest, persistent fever, cough
Arterial oxygen tension (PaO2) at rest, room air
> 11.0 kPa (> 82.5 mmHg)
8.1-11.0 kPa (60.75-82.5 mmHg)
< 8.0 kPa (< 60 mmHg)
SaO2 (SaO₂) at rest, room air
> 96%
91-96%
< 91%
CXR
Normal or minor perihilar shadowing
Diffuse interstitial shadowing
Extensive interstitial shadowing with or without diffuse alveolar shadowing
PCP severity cannot be accurately assessed
Diagnostic investigations
Respiratory tract specimen testing: as per BHIVA 2024 guidelines, obtain immunofluorescence, histochemistry, or PCR of induced sputum or bronchoalveolar lavage for the diagnosis of PCP.
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Blood tests
Chest imaging
Respiratory support
Medical management
First-line antimicrobial therapy: as per DHHS 2025 guidelines, administer TMP/SMX 15-20/75-100 mg/kg/day PO in 3 divided doses or 2 double-dose tablets TID
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for a total duration of 21 days B
as the preferred therapy in patients with mild-to-moderate PCP. A
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Second-line antimicrobial therapy
Adjunctive corticosteroids (HIV-positive)
Adjunctive corticosteroids (HIV-negative)
Antiretroviral therapy
Management of drug adverse events
Specific circumstances
Pregnant patients, prophylaxis: as per DHHS 2025 guidelines, consider discussing the option of deferring pregnancy until PCP prophylaxis can be safely discontinued (CD4 count > 200 cells/mcL for 3 months) with patients planning to become pregnant.
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Pregnant patients (antimicrobial therapy)
Pregnant patients (folic acid supplementation)
Pregnant patients (adjunctive corticosteroids)
Pregnant patients (monitoring)
Preventative measures
Isolation: as per DHHS 2025 guidelines, insufficient evidence to recommend isolating patients at high risk for PCP from patients with known PCP to prevent transmission.
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Primary prophylaxis (indications, HIV)
Primary prophylaxis (indications, immunosuppressive therapy)
Primary prophylaxis (first-line regimens)
Primary prophylaxis (alternative regimens)
Primary prophylaxis (discontinuation)
Secondary prophylaxis (initiation)
Secondary prophylaxis (first-line regimens)
Secondary prophylaxis (alternative regimens)
Secondary prophylaxis (discontinuation)