Affiliations: Kawasaki Medical School
Kawasaki Medical School Kawasaki Hospital
Okayama, Japan;Correspondence to: Naoyuki Miyashita, MD, PhD, Division of Respiratory Diseases, Department of Medicine, Kawasaki Medical School, Matsushima 577, Kurashiki City, Okayama 701-0192, Japan; e-mail: firstname.lastname@example.org,
Kurashiki Central Hospital
To the Editor:
We read with great interest the article by Ishida et al
(December 1998)1regarding their investigation of the
etiology of community-acquired pneumonia (CAP) among the Japanese
population for the first time and their finding that Chlamydia
pneumoniae was identified in 3.4% of episodes by using the
enzyme-linked immunosorbent assay (ELISA). Of these patients, two
(18.1%) had dual infections. In several recent CAP studies, however,
C pneumoniae has been found to account for up to 10% of
CAP cases in Western countries.3 Furthermore, C
pneumoniae has been reported to cause pneumonia frequently in
association with other microorganisms, mainly Streptococcus
pneumoniae.,3–4 We would like to expand these
observations with our findings, using the traditional diagnostic
methods for detection of C pneumoniae.
We undertook a study to determine the etiology of CAP in Japan
between April 1998 and July 1999. Traditional diagnostic methods,
including paired serum samples for the microimmunofluorescence test to
detect C pneumoniae, were used in combination with cell
cultures for isolation of C pneumoniae. Culture for
C pneumoniae was performed in cycloheximide-treated
Nine out of 112 patients (8.0%) received diagnoses of C
pneumoniae by this method. Serologic criteria established the
diagnosis in nine cases and isolated the bacteria in two.
Culture-positive specimens were also found to be positive by serology.
Of these patients, five had polymicrobial infections, which were
associated with S pneumoniae in two cases,
Legionella pneumophila in one, Haemophilus
influenzae in one, and S pneumoniae and
Staphylococcus aureus in one. One of these patients
died. The mean length of hospitalization of these five patients with
mixed C pneumoniae pneumonia was significantly longer
than that of patients with C pneumoniae monoinfection or
those with non-C pneumoniae pneumonia (45.2 days vs 16.9
days). It has been noted that mixed infection with C
pneumoniae and other microorganisms often increases symptoms
and even mortality.3–4 This was also observed in our
study, especially in the patients infected with C
pneumoniae and S pneumoniae.
We found C pneumoniae in 8.0% of the CAP cases using
specific methods, and the clinical results were comparable with those
of recent reports in Western countries.3–4 Therefore, we
believe that, in addition to S pneumoniae, C
pneumoniae is also an important pathogen among the Japanese
population, and we believe that diagnostic tests must be readily
available for early recognition of C pneumoniae
We thank Dr. Miyashita and colleagues for their interest in our
article (December 1998).1 In our study, screening for
Chlamydia pneumoniae was chiefly conducted using
enzyme-linked immunosorbent assay (ELISA). However, because it often
takes several weeks to recognize the significant elevation of antibody
titer, there may have been patients with conditions that could not be
diagnosed using ELISA while hospitalized and who were not followed
after discharge. It is therefore possible that the actual incidence of
C pneumoniae pneumonia was slightly higher among all
community-acquired pneumonia (CAP) cases. The incidence of C
pneumoniae pneumonia may also have differed because of the year in
which the survey was conducted.
We conducted a separate prospective multicenter study of the etiology
of CAP at three hospitals in Japan2 and diagnosed C
pneumoniae pneumonia in 7.9% of all cases. Statistics kept
independently by our hospital over the past 5 years show that C
pneumoniae pneumonia accounted for 33 (6.0%) of all 552 CAP
cases, and was the fourth leading causative organism after
Streptococcus pneumoniae, Haemophilus influenzae, and
Mycoplasma pneumoniae. Of the 33 C pneumoniae
pneumonia patients, 10 had dual infections involving another pathogenic
organism. As also pointed out by Dr. Miyashita and colleagues, C
pneumoniae appears to be an important cause of CAP in Japan as it
is in Western countries. However, we often find difficulty in
diagnosing C pneumoniae pneumonia, so the widespread
availability of a simple and rapid diagnostic method is needed.
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