Pneumocystis Jiroveci (Previously Known as Pneumocystis Carinii Pneumonia)



Opportunistic lung infection caused by Pneumocystis jiroveci. This organism is currently considered a primitive fungus based on DNA sequence analysis. It has two developmental forms (the cysts contain sporozoites that become trophozoites when excised).

  • Although previously known as Pneumocystis carinii pneumonia (PCP), the acronym PCP is still in use and refers to Pneumocystis pneumonia.
  • PCP occurs almost exclusively in the immunocompromised host.
  • PCP is an AIDS-defining illness. It is the most common opportunistic life-threatening lung infection in infants with perinatally acquired HIV disease.
  • P. jiroveci causes a diffuse pneumonitis characterized by fever, dyspnea at rest, tachypnea, hypoxemia, nonproductive cough, and bilateral diffuse infiltrates in the roentgenogram. It is a severe condition frequently leading to respiratory failure, necessitating intubation and mechanical ventilation.
  • Chemoprophylaxis against this microorganism has proven successful. Therefore, early identification of the HIV-infected mother becomes essential.
  • Despite advances in therapy, the infection continues to be associated with significant morbidity and mortality.


  • Ubiquitous in mammals worldwide, particularly rodents
  • Growth on respiratory tract surfaces
  • Mode of transmission is unknown:
    • Airborne person-to-person transmission is possible, but case contacts are rarely identified.
    • Environmentally acquired
  • Asymptomatic infection appears early in life; >70% of healthy individuals have antibodies by age 4 years.
  • Primary infection is likely to be the mechanism in infants. Reactivation of latent disease with immunosuppression was proposed as an explanation for disease later in childhood; however, animal models of PCP do not support this proposition.
  • PCP in the HIV patient can occur at any time but usually presents during the 1st year of life. The highest incidence is between 3 and 6 months of age.


Immunocompromised host

  • Children with congenital or acquired AIDS and recipients of suppressive therapy in the treatment of malignancies or after organ transplantation are at high risk.
  • In leukemic patients, the incidence of PCP has been directly related to the degree of immunodeficiency resulting from chemotherapy.
  • Epidemics of PCP were reported in premature and malnourished infants and children in resource-limited countries and during times of famine.


  • Chemoprophylaxis indications: During high-risk periods, PCP can be effectively prevented in the immunodeficient host by chemoprophylaxis in the following groups:
    • HIV exposed: 4 to 6 weeks to 4 months
    • HIV infected or indeterminate: 4 to 12 months
    • HIV infected: 1 to 5 years if CD4+ T-lymphocyte count is <500 cells/μL or <15%
    • HIV infected: ≥6 years if CD4+ T-lymphocyte count is <200 cells/μL or <15%
    • Severely symptomatic HIV patients or those with rapidly declining CD4 counts
    • HIV patients who have had previous PCP illness
    • Children who have received hematopoietic stem cell transplants (HSCTs)
    • All HSCT recipients with hematologic malignancies (e.g., leukemia, lymphoma)
    • All HSCT recipients receiving intense conditioning regimens or graft manipulation
      • Prophylaxis is initiated at engraftment and administered for 6 months; longer than 6 months in children receiving immunosuppressive therapy or with chronic graft-versus-host disease
  • Drug regimen for prophylaxis
    • Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice.
      • 150 mg/m2 body surface area per day of TMP or 750 mg/m2 body surface area per day of SMX PO divided into 2 doses on 3 consecutive days per week
      • TMP-SMX can also be given 7 days a week when prevention against other bacterial infections is sought.
    • For patients who cannot tolerate TMP-SMX
      • Dapsone (>1 month of age): 2 mg/kg (maximum 100 mg) PO daily or 4 mg/kg (maximum 200 mg) PO weekly
      • Aerosolized pentamidine (>5 years of age): 300 mg via Respirgard II nebulizer inhaled monthly
      • Atovaquone at age 1 to 3 months and >24 months: 30 mg/kg (maximum 1,500 mg/dose) PO daily; at age 4 to 24 months: 45 mg/kg (maximum 1,500 mg/dose) PO daily


  • In the immunodeficient child, the pathologic changes occur predominantly in the alveoli. Cysts and trophozoites are seen adhering to the alveolar lining cells or in the cytoplasm of macrophages.
  • As infection progresses, the alveolar spaces are filled with a pink, foamy exudate containing fibrin, abundant desquamative cells, and a large number of organisms. Alveolar septal thickening with mononuclear cell infiltration is also seen.

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