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Pneumocystis jirovecii Pneumonia (PJP)

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Pneumocystis jirovecii pneumonia (PJP)

Pneumocystis jirovecii pneumonia (PCP) is an opportunistic fungal pneumonia caused by Pneumocystis jirovecii, occurring mainly in immunocompromised individuals.

Also called

PCP (Pneumocystis pneumonia)

ICD-10

B44.81

Specialty

Pulmonology

Onset

Acute

Reviewed

July 2026

On This Page

Overview

  • Pneumocystis Pneumonia (PJP) is one of the most common opportunistic infections in patients with:

    • HIV/AIDS
    • Organ transplantation
    • Hematologic malignancies
    • Long-term immunosuppressive therapy

    The infection causes:

    Diffuse alveolar inflammation → Impaired gas exchange → Progressive hypoxemia

Etiology & Risk Factors

Cause

  • Pneumocystis jirovecii

Risk Factors

  • HIV/AIDS (especially CD4 <200 cells/μL)
  • Prolonged corticosteroid therapy
  • Organ transplantation
  • Hematologic malignancies
  • Chemotherapy
  • Immunosuppressive medications
  • Primary immunodeficiency

Important Note

Pneumocystis Pneumonia (PJP) should always be suspected in immunocompromised patients with progressive dyspnea, dry cough, and hypoxemia.

Pathophysiology

Immunosuppression
⬇
Pneumocystis jirovecii infection
⬇
Diffuse alveolar colonization
⬇
Alveolar inflammation
⬇
Protein-rich foamy alveolar exudate
⬇
Impaired oxygen diffusion
⬇
Progressive hypoxemia
⬇
Respiratory failure (severe disease)

Key Concept

PJP causes diffuse alveolar injury resulting in severe hypoxemia rather than focal lobar consolidation.

Clinical Presentation

  • Symptoms

    • Progressive dyspnea
    • Dry cough
    • Fever
    • Fatigue
    • Reduced exercise tolerance
    • Chest discomfort

    Signs

    • Tachypnea
    • Tachycardia
    • Reduced oxygen saturation
    • Fine inspiratory crackles (may be absent)

    Severe Disease

    • Marked hypoxemia
    • Cyanosis
    • Respiratory distress
    • Respiratory failure

History Taking

    • Ask about:

      • HIV infection?
      • CD4 count?
      • Organ transplantation?
      • Long-term corticosteroid use?
      • Immunosuppressive medications?
      • Progressive shortness of breath?
      • Dry cough?
      • Fever?
      • Weight loss?
      • Previous PJP?
      • PJP prophylaxis?

Physical Examination

Look for:

  • Fever
  • Tachypnea
  • Tachycardia
  • Hypoxemia
  • Cyanosis

Chest Examination

May show:

  • Fine inspiratory crackles
  • Normal examination in early disease

Investigations of Pneumocystis Pneumonia (PJP)

  • Chest Imaging

    Chest X-ray

    May show:

    • Diffuse bilateral interstitial or perihilar infiltrates

    May be normal early in the disease.

    High-Resolution CT (HRCT)

    May show:

    • Diffuse bilateral ground-glass opacities
    • Interstitial infiltrates
    • Pulmonary cysts (occasionally)

    Laboratory Tests

    • CBC
    • LDH (often elevated)
    • HIV testing when appropriate
    • Arterial blood gas

    Microbiological Diagnosis

    Obtain respiratory specimens for:

    • PCR for Pneumocystis jirovecii
    • Microscopy with special stains
    • Bronchoalveolar lavage (BAL) if sputum is nondiagnostic

Diagnosis of Pneumocystis Pneumonia (PJP)

1. Compatible Clinical Features

  • Progressive dyspnea
  • Dry cough
  • Fever

2. Compatible Imaging

  • Bilateral diffuse infiltrates
  • Ground-glass opacities

3. Microbiological Confirmation

Using:

  • PCR
  • Microscopy
  • Bronchoalveolar lavage specimens

Important Note

Definitive diagnosis requires identification of Pneumocystis jirovecii in respiratory specimens.

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Related Topics

Management of Pneumocystis Pneumonia (PJP)

  • Main Goals

    • Eradicate infection
    • Improve oxygenation
    • Prevent respiratory failure
    • Treat underlying immunosuppression

    First-Line Therapy

    • Trimethoprim-sulfamethoxazole (TMP-SMX)

    Adjunctive Corticosteroids

    Recommended for moderate-to-severe PJP with significant hypoxemia.

    Supportive Management

    • Oxygen therapy
    • Mechanical ventilation if required
    • Optimize treatment of the underlying immunodeficiency

    Prevention

    TMP-SMX prophylaxis is recommended for high-risk patients (e.g., HIV with CD4 <200 cells/μL).

Complications of Pneumocystis Pneumonia (PJP)​

  • Acute respiratory failure
  • Acute respiratory distress syndrome (ARDS)
  • Pneumothorax
  • Secondary bacterial infection
  • Mechanical ventilation
  • Death

Prognosis of Pneumocystis Pneumonia (PJP)

  • Prognosis is excellent with early diagnosis and treatment.
  • Delayed diagnosis increases mortality.
  • Prognosis is worse in:
    • Severe hypoxemia
    • Delayed treatment
    • Non-HIV immunocompromised patients
  • Appropriate prophylaxis markedly reduces the incidence of PJP.

Key Points / Clinical Pearls

  • Pneumocystis jirovecii pneumonia (PJP)​ is an opportunistic fungal pneumonia caused by Pneumocystis jirovecii.
  • It occurs mainly in immunocompromised patients, especially those with HIV/AIDS (CD4 <200 cells/μL).
  • Progressive dyspnea, dry cough, fever, and hypoxemia are classic features.
  • HRCT typically shows diffuse bilateral ground-glass opacities.
  • Chest X-ray may be normal early in the disease.
  • PCR or microscopy of respiratory specimens confirms the diagnosis.
  • TMP-SMX is the first-line treatment and prophylaxis.
  • Adjunctive corticosteroids are indicated in moderate-to-severe PJP with hypoxemia.
  • Pneumothorax is a recognized complication of PJP.