Opportunistic pneumonia caused by Pneumocystis jirovecii in HIV/AIDS and other immunocompromised hosts; presents with dyspnea, dry cough, and hypoxia.
Also known as: PCP, PJP, Pneumocystis pneumonia, Pneumocystis carinii pneumonia, Pneumocystis jirovecii
Overview
Opportunistic pulmonary infection caused by the fungus Pneumocystis jirovecii (formerly Pneumocystis carinii). Hallmark of advanced HIV/AIDS but also affects other immunocompromised patients including solid organ transplant recipients, patients on chronic corticosteroids, and those receiving immunosuppressive chemotherapy.
Epidemiology
Most cases in HIV-infected patients with CD4 <200 cells/microL. Incidence in HIV has declined dramatically with antiretroviral therapy and TMP-SMX prophylaxis. In non-HIV immunocompromised hosts (transplant, hematologic malignancy, vasculitis on steroids), PCP often presents more acutely and with higher mortality.
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Malnutrition in infants and severely debilitated adults
Pathophysiology
Pneumocystis is acquired through inhalation and persists in human lungs; clinical disease results from defective cell-mediated immunity. Organisms adhere to type I pneumocytes, causing diffuse alveolar damage, foamy intra-alveolar exudate, and surfactant abnormalities. Inflammation and impaired gas exchange produce hypoxia disproportionate to chest x-ray findings.
Clinical presentation
Symptoms
HIV-associated: subacute progressive dyspnea, dry nonproductive cough, low-grade fever, fatigue, weight loss over weeks
Non-HIV immunocompromised: more abrupt onset (days), higher fevers, more severe hypoxia
Pleuritic chest pain is uncommon
Hemoptysis is uncommon
Asymptomatic carriage occurs
Signs / physical exam
Tachypnea, tachycardia
Hypoxia disproportionate to chest auscultation findings
Lung exam often surprisingly clear or with diffuse fine crackles
Oral thrush is common in HIV-associated disease
Exertional desaturation on ambulation is sensitive in early disease
Classic findings
HIV patient with CD4 <200, subacute dry cough, hypoxia disproportionate to a chest x-ray showing bilateral perihilar interstitial or ground-glass infiltrates. Markedly elevated LDH and beta-D-glucan.
Differential diagnosis
Bacterial pneumonia — Lobar consolidation, productive cough, leukocytosis; responds to standard antibiotics
Viral pneumonia (influenza, COVID-19, RSV, CMV in transplant) — Bilateral infiltrates, similar imaging; viral PCR, CMV PCR
Definitive diagnosis: identification of Pneumocystis by direct fluorescent antibody, GMS, Giemsa, or PCR on respiratory specimen. Presumptive treatment may be initiated based on clinical and radiographic picture in classic settings while awaiting confirmation.
Labs
ABG (or pulse oximetry with ambulation) — degree of hypoxia drives adjunctive steroid use
LDH (often markedly elevated)
Beta-D-glucan (sensitive but not specific)
HIV testing and CD4 count if not known
Induced sputum with silver stain (GMS), DFA, or PCR for Pneumocystis
Bronchoalveolar lavage (BAL) with PCR or staining if induced sputum negative or non-diagnostic — gold standard sensitivity
CBC, BMP, LFTs prior to TMP-SMX (renal function, baseline LFTs)
Imaging
Chest x-ray: bilateral perihilar reticular or ground-glass infiltrates; may be normal early in disease
Chest CT (more sensitive): diffuse ground-glass opacities with relative subpleural sparing, occasional cysts and pneumothorax
Findings of upper-lobe disease with pneumatoceles and pneumothorax classically associated with aerosolized pentamidine prophylaxis
Diagnostic algorithm
flowchart TD
A[Immunocompromised host<br/>HIV CD4 <200,<br/>steroids, transplant] --> B[Subacute dyspnea<br/>dry cough, hypoxia]
B --> C[CXR / CT: bilateral<br/>ground-glass infiltrates]
C --> D[LDH high, beta-D-glucan +]
D --> E[Induced sputum / BAL<br/>GMS, DFA, PCR]
E --> F[TMP-SMX x 21 days]
F --> G{PaO2 <70 or<br/>A-a >=35?}
G -->|Yes| H[Add prednisone taper<br/>40 BID x 5, 40 x 5, 20 x 11]
G -->|No| I[TMP-SMX alone]
F --> J[Secondary prophylaxis<br/>until CD4 >200 x 3 mo on ART]
PCP diagnostic and treatment pathway including adjunctive steroid indications.
Treatment
First-line
Trimethoprim-sulfamethoxazole (TMP-SMX) 15-20 mg/kg/day of TMP component IV or PO divided every 6-8 hours for 21 days — first-line for all severities
Adjunctive corticosteroids if PaO2 <70 mmHg on room air OR A-a gradient >=35 mmHg: prednisone 40 mg PO BID x 5 days, then 40 mg daily x 5 days, then 20 mg daily x 11 days (improves mortality in moderate to severe HIV-associated PCP)
Supportive care: supplemental oxygen, mechanical ventilation if needed
Initiate or continue antiretroviral therapy in HIV (no specific delay required for PCP, in contrast to cryptococcal meningitis)
Second-line / adjunct
Sulfa allergy or TMP-SMX intolerance — choose by severity:
Mild-moderate: dapsone-trimethoprim OR clindamycin-primaquine OR atovaquone
Severe: IV pentamidine 4 mg/kg/day or clindamycin-primaquine
G6PD testing prior to dapsone or primaquine (both cause hemolysis in G6PD deficiency)
Echinocandins (caspofungin) have weak activity and are NOT recommended as primary therapy
Secondary prophylaxis until CD4 >200 for >3 months on ART: TMP-SMX 1 single-strength or DS tablet daily; alternatives include dapsone, atovaquone, or aerosolized pentamidine
Drug toxicity from TMP-SMX: rash, fever, neutropenia, hyperkalemia, AKI, hepatitis
Treatment failure and mortality higher in non-HIV immunocompromised hosts
Immune reconstitution inflammatory syndrome (IRIS) if ART started concurrently — usually mild
PANCE pearls
TMP-SMX is the unambiguous first-line treatment AND prophylaxis for PCP at all severities — sulfa allergy must be carefully verified.
Adjunctive corticosteroids are mortality-reducing when PaO2 <70 mmHg or A-a gradient >=35 mmHg in HIV-associated PCP — do not forget to add them.
LDH and beta-D-glucan are useful supportive labs but neither establishes nor excludes diagnosis.
Indications for primary PCP prophylaxis in HIV: CD4 <200 cells/microL, history of oropharyngeal candidiasis, or AIDS-defining illness.
Echinocandins (caspofungin) do not reliably treat PCP and should not be used as primary therapy.
References
AIDSinfo / NIH / HHS — Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents with HIV — Pneumocystis jirovecii pneumonia section
CDC — CDC — Pneumocystis pneumonia: epidemiology, diagnosis, and treatment
ATS / IDSA — Diagnosis and treatment of pneumonia in immunocompromised hosts (consensus statements)
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