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Pneumocystis pneumonia
(PCP) occurs almost exclusively in the severely immunocompromised
host, especially patients with congenital immunodeficiency diseases,
AIDS, and cancer, and those who have had organ transplantation. Once
pneumonia is apparent, the fatality rate is near 100% if
untreated. Effective therapeutic and prophylactic drugs are available. The
causative agent is a protozoan-like fungus known for the past century
as Pneumocystis carinii. Recently, the term Pneumocystis
jirovecii has been proposed for the organism found in humans,1 but
acceptance has not been universal.2
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Pneumocystis infection is recognized among humans
and lower animals worldwide. The natural habitat and mode of transmission
in man are unknown, but animal studies suggest animal-to-animal
transmission occurs by the airborne route.3-5 Animal-to-human
transmission has not been reported, and available evidence suggests
that human-to-human transmission is possible.11 Symptomatic
infection occurs sporadically in immunocompromised individuals.
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PCP was first recognized in humans by Van der Meer and Brug in 1942.6 During
this time, epidemics of interstitial plasma cell pneumonitis were
occurring in European infants. In the 1950s, several reports confirmed
that Pneumocystis was the etiology of epidemics
of interstitial plasma cell pneumonitis in European infants.7
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With the advent of immunosuppressive therapy for cancer and methods
for diagnosing congenital immunodeficiency disorders, PCP became
recognized as a potentially fatal infection in such individuals.8-10
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Intrauterine transmission of Pneumocystis has
also been reported.12,13 Of eight pregnant women with AIDS
and PCP, one infant had Pneumocystis infection.14,15 Considerable
data show that at least 75% of normal children reaching
4 years of age have acquired antibody to Pneumocystis and
that more than 90% of normal adults have detectable antibody.16-18,19 Furthermore,
a prospective study of otherwise normal infants, ages 2 to 12 weeks,
with pneumonia showed that 10 of 69 babies had detectable antibody
to Pneumocystis and that one of the 10 infants
had PCP.20 In serial observations of 107 normal infants, Pneumocystis DNA
was detected in nasopharyngeal aspirates in 74 of the infants tested.21 In
addition, Pneumocystis has been associated with
sudden infant death syndrome (SIDS), but no cause and effect has
been proven.22,23 The natural course of PCP can be delineated
from studies done before the advent of chemoprophylaxis in 1977
in individuals at high risk for PCP. Data collected at the Centers
for Disease Control (CDC) revealed 194 documented cases of PCP encountered
in the United States during the 3-year period from 1967 to 1970.
Twenty-five (12.9%) of these cases had primary immunodeficiency
disorders; 91 (47%) had leukemia; 41 (21%) had
other malignancies; 22 (11%) were organ transplant recipients,
and 15 (8%) had other immunocompromising conditions.24-26From
1962 to 1971, the incidence of PCP was determined in 1251 children
with malignancies and 379 patients with nonmalignant neoplasms or
immunodeficiency diseases at St. Jude Children’s Research
hospital; PCP was found in 4.1%, 0%, and 0% ...