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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

-General 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.