Pneumonia, Pneumocystis Jiroveci (PCP)

BASICS

Definition: Pneumonia caused by Pneumocystis jiroveci, formerly known as P. carinii (hence, PCP).
Organism: Fungus unique to humans; resistant to most antifungals (including amphotericin and azoles).
System affected: Primarily affects immunocompromised hosts.
No combination of clinical findings is diagnostic; diagnosis relies on direct detection of organism.

HIV-infected adults: Start when CD4 <200/µL or oropharyngeal candidiasis
HIV-infected children:
≥6 years: same as adults
1–5 years: start when CD4 <500/µL
Infants: prophylaxis for first year of life (start at 4–6 weeks)
Non-HIV immunocompromised: Prophylaxis is recommended; specific guidelines for start/end timing not established

HIV: Stop after ≥6 months of ART with sustained CD4 >200/µL for >3 months (children: >500/µL for 1–5 years old)
Non-HIV: Discontinue as per immune reconstitution

HIV: Subacute, progressive dyspnea, tachypnea, dry cough, low-grade fever, malaise, weakness
Non-HIV immunocompromised: More acute onset, rapid progression, fulminant respiratory failure

Cannot culture organism—diagnosis is by direct detection (immunofluorescent stains, PCR)
Labs:
ABG: Hypoxemia, ↑ A–a gradient
LDH: Often elevated (nonspecific)
CD4 <200/µL (HIV)
Imaging:
CXR: Bilateral, symmetric, fine, reticular interstitial infiltrates, perihilar; may progress to diffuse opacities; up to 30% normal CXR
CT: High-res CT more sensitive
Procedures:
Fiberoptic bronchoscopy with BAL (best for direct organism detection by DFA stain)
PCR: Sensitive but false positives possible

TMP-SMX (preferred): 15–20 mg/kg/day (TMP) PO/IV in 3–4 divided doses × 21 days (reduce dose in renal failure)
Pediatrics (>2 months): TMP 15–20 mg/kg/day in divided doses q6–8h

Pentamidine (IV): 4 mg/kg daily (reserved for moderate-severe cases; greater toxicity)
Dapsone + trimethoprim (adults): Dapsone 100 mg PO QD + TMP 5 mg/kg PO TID (check G6PD)
Clindamycin + primaquine (adults): Clindamycin 900 mg IV q8h + Primaquine 30 mg PO QD
Atovaquone: 750 mg PO BID (>13 yrs); children: 40 mg/kg/day PO divided BID (max 1,500 mg)

Corticosteroids (for moderate-severe PCP in HIV with PaO2 <70 mmHg or A–a gradient >35 mmHg):
Prednisone: 40 mg PO BID days 1–5, 40 mg QD days 6–11, 20 mg QD days 12–21

No fixed criteria, but consider for hypoxemia, severe respiratory distress, or rapid progression.
Prognostic factors (HIV):
Older age
IV drug use
Total bilirubin >0.6 mg/dL
Serum albumin <3 g/dL
A–a O2 gradient ≥50 mmHg

Secondary prophylaxis: Required for all HIV patients with history of PCP unless sustained CD4 >200/µL for ≥3 months on ART
Monitor: LDH, PFTs, ABG for response
Patient education: Continue ART, adhere to prophylaxis

HIV-infected infants: High mortality without treatment
Non-HIV immunosuppressed: Acute onset, higher mortality if diagnosis/treatment delayed
Good prognosis with early diagnosis/treatment in adults

PCP only occurs in immunocompromised patients (esp. HIV with CD4 <200/µL)
Colonization common in children but rarely causes disease in immunocompetent hosts
Prophylaxis: TMP-SMX, start when CD4 <200/µL, discontinue after sustained recovery with ART
First-line treatment: TMP-SMX for 21 days (HIV); 14 days (non-HIV)
Corticosteroids benefit hypoxemic HIV patients
Bronchoscopy with BAL is the gold standard for diagnosis