Description

• Pneumocystis jiroveci causes pneumonia primarily in immunocompromised patients.
• The fungus that causes this pneumonia in humans was previously called Pneumocystis carinii.
• The name was formally changed to Pneumocystis jiroveci in 2001, following the discovery that the fungus that infects humans is unique and distinctive from the fungus that infects animals.
• P. jiroveci is extremely resistant to traditional antifungal agents, including both amphotericin and azole agents.
• To prevent confusion, the term PCP, which used to represent P. carinii pneumonia, now represents Pneumocystis pneumonia (1).

Epidemiology

• P. jiroveci has a worldwide distribution, and most children have been exposed to the fungus by 2 to 4 years (3).
• The reservoir and mode of transmission for P. jiroveci is still unclear.
  • Human studies favor an airborne transmission model, with person-to-person spread being the most likely mode of infection acquisition (2).

Incidence

• Infants with HIV infection have a peak incidence of PCP between 2 and 6 months (3).
• HIV-infected infants have a high mortality rate, with a median survival of only 1 month.

Prevalence

• The prevalence of P. jiroveci colonization among healthy adults is 0–20%.
• Recent studies have demonstrated the transient nature of P. jiroveci colonization in asymptomatic, immunocompetent patients (2).
• 50% of patients with PCP are coinfected with ≥2 strains of P. jiroveci (3).
• There is evidence that distinct strains are responsible for each episode in patients who develop multiple episodes of PCP (3).

Etiology and Pathophysiology

Mode of transmission is unknown; likely respiratory from infected host

Risk Factors

Individuals at risk (2)

• Patients with HIV infection, especially if not receiving prophylactic treatment for PCP
• Patients who are receiving high doses of glucocorticoids
• Patients who have an altered immune system not due to HIV
• Patients who are receiving chronic immunosuppressive medications
• Patients who have hematologic or solid malignancies resulting in malignancy-related immune depression

General Prevention

• Indications for prophylaxis
  • HIV-infected adults (3)
    • Should start when CD4 count is <200 cells/μL or if the patient develops oropharyngeal candidiasis
  • HIV-infected children (3)
    • Prophylaxis should be provided for children ≥6 years based on adult guidelines.
    • For children aged 1 to 5 years, start when CD4 count is <500 cells/μL.
    • For infants <12 months, start when the CD4 percentage is <15%.
  • Non–HIV-infected adults receiving immunosuppressive medications or with underlying immune system deficits should receive PCP prophylaxis, but currently, there are no specific guidelines on when to start this.
• Medication
  • Trimethoprim-sulfamethoxazole (TMP-SMX)
    • Adults: 1 double-strength tablet daily or 1 double-strength tablet 3 times per week
    • Children >2 months: TMP 150 mg/kg/day in divided doses q12h for 3 days/week
  • Atovaquone suspension
    • Adults: 1,500 mg PO once daily with food
    • Children: not to exceed 1,500 mg/day
      • 1 to 3 months: 30 mg/kg/day PO once daily
      • 4 to 24 months: 45 mg/kg/day PO once daily
      • >24 months: 30 mg/kg/day PO once daily
      • Adolescents ≥13 years: Refer to adult dosing.
  • Dapsone
    • Adults only: 50 mg BID or 100 mg once daily
  • Pentamidine
    • Adults only: 300 mg aerosolized every 4 weeks
• Discontinuation of prophylaxis
  • When CD4+ cell counts are >200 cells/μL for a period of 3 months in the adult population
  • There are no clear guidelines for discontinuation of prophylaxis in children.

Commonly Associated Conditions

• HIV Infection
• Chronic obstructive pulmonary disease (COPD)
• Interstitial lung disease
• Connective tissue diseases treated with corticosteroids
• Cancer and organ transplant patients on immunosuppressive medication