Pneumonia, Pneumocystis Jiroveci

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Basics

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).

ALERT
No combination of symptoms, signs, blood chemistries, or radiographic findings is diagnostic of P. jiroveci pneumonia (2).

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

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