Kawasaki Medical School
Correspondence to: Naoyuki Miyashita, MD, PhD, Department of Internal Medicine, Kurashiki Daiichi Hospital, 5–3-10 Oimatsu cho, Kurashiki City, Okayama 710-0826, Japan; e-mail: firstname.lastname@example.org
To the Editor:
Community-acquired pneumonia (CAP) remains a common cause of
morbidity. Because CAP also is a potentially fatal disease, even in
previously healthy persons, early appropriate antibiotic treatment is
vital. In Japan, pneumonia is the fourth leading cause of death, and
from 57 to 70 persons per 100,000 population died per year of this
disease in the last decade. Because of this high rate of morbidity,
guidelines for CAP management have been produced in
Japan.1However, prospective studies on the etiology of
CAP among the Japanese population have been very limited, and only the
etiology of CAP has been investigated by Ishida et al (December
1998).2 Therefore, we investigated the etiology of CAP
requiring hospitalization in Japan based on our findings.
We undertook a study to determine the etiology of CAP in Japan between
April 1998 and September 2000 at three different hospitals. The
microbiological and serologic studies that were performed were almost
the same as those used in the study by Ishida et al.2 In
addition, we also employed other diagnostic methods for the detection
of Chlamydia spp, Coxiella burnetii, and Legionella spp.
Chlamydia pneumoniae, Chlamydia psittaci, and
Chlamydia trachomatis infections were diagnosed by isolation
in cell cultures and by serology. Antibodies to Chlamydia spp were
measured by the microimmunofluorescence test, and cell cultures were
performed in cycloheximide-treated HEp-2 and HeLa 229 cells. Antibodies
to C burnetii were measured by the indirect
immunofluorescence test. In addition to serology and culturing, the
urinary antigen test was used for detection of Legionella spp.
Two hundred patients (128 men and 72 women; age range, 19 to 91 years;
mean age, 60.9 years) who had had episodes of pneumonia were enrolled
in the study. One hundred nine (54.5%) patients had at least one
underlying disease. A microbiological diagnosis was established in 117
patients with pneumonia (58.5%). The most common pathogens were
Streptococcus pneumoniae (41 patients [20.5%]), followed
by Haemophilus influenzae (22 patients [11.0%]),
Mycoplasma pneumoniae (19 patients [9.5%]), C
pneumoniae (15 patients [7.5%]), and Staphylococcus
aureus (10 patients [5.0%]) (Table 1
). Dual pathogens were detected in 25 patients (12.5%).
Ishida et al2 investigated the etiology of CAP among the
Japanese population for the first time, and their findings did not
differ markedly when compared with those of Western countries. Our
results were almost consistent with those of Ishida et
al,2with the exception of the frequencies of atypical
pathogens. The atypical pathogens, C pneumoniae, Legionella
spp, C burnetii, and M pneumoniae, have been
recognized as common respiratory pathogens. In several
studies,6 these organisms have been found to account
for up to 25% of CAP cases in Western countries. In the present study,
we were able to detect atypical pathogens in approximately 20% of CAP
cases. The frequencies were lower than those in Western countries but
were higher than those in the study of Ishida et al.2 The
difference from the study by Ishida et al may be related to the period
in which the survey was conducted or to the traditional diagnostic
methods used for the detection of C pneumoniae. The
difference from findings in Western countries may be due to the low
incidence of Legionella and C burnetii pneumonia in Japan.
In our study, S pneumoniae was the leading cause of CAP, and
an emerging or newly recognized pathogen, C pneumoniae, was
also a significant causative microorganism in Japan. The recognition of
these results will allow us to treat patients with prompt antimicrobial
therapy and will promote the formulation of new guidelines for the
management of CAP in Japan.
Patients with dual infections were
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