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Journal of Clinical Microbiology, November 2008, p. 3808-3810, Vol. 46, No. 11
0095-1137/08/$08.00+0 doi:10.1128/JCM.01782-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Serotype Distribution and Penicillin Resistance of Streptococcus pneumoniae Isolates from Middle Ear Fluids of Pediatric Patients with Acute Otitis Media in Japan 
Muneki Hotomi,1
Dewan S. Billal,1
Yosuke Kamide,2
Keiko Kanesada,3
Yoshifumi Uno,4
Fumiyo Kudo,5
Masato Ito,6
Seiji Kakehata,7
Rinya Sugita,8
Masashi Ogami,1
Noboru Yamanaka,1* for the Advanced Treatment for Otitis Media Study Group (ATOMS)
Department of Otolaryngology, Head and Neck Surgery, Wakayama Medical University, Wakayama, Japan,1
Kamide ENT Clinic, Shizuoka, Japan,2
Nonohana Clinic, Yamaguchi, Japan,3
Uno ENT Clinic, Okayama, Japan,4
Chiba College of Public Health, Chiba, Japan,5
Department of Otolaryngology, Head and Neck Surgery, Kanazawa University, Kanazawa, Japan,6
Department of Otolaryngology, Head and Neck Surgery, Hirosaki, University, Hirosaki, Japan,7
Sugita ENT Clinic, Chiba, Japan8
Received 16 September 2008/
Accepted 18 September 2008

ABSTRACT
Out of 175 pneumococcal isolates from middle ear fluids, 26.3%
were penicillin-resistant
S. pneumoniae (PRSP). Serotypes 19F
and 23F occurred most frequently among PRSP strains. The 7-valent
pneumococcal conjugate vaccine (PCV) showed better coverage
of PRSP strains (87.0%). The 7-valent PCV may reduce the prevalence
of PRSP in Japan.

TEXT
Acute otitis media (AOM) is one of the leading infectious diseases
caused by
Streptococcus pneumoniae (
3,
9). In recent decades,
penicillin-resistant
S. pneumoniae (PRSP) has evolved into a
global problem, especially with AOM (
7,
12,
18,
21). The 7-valent
pneumococcal conjugate vaccine (PCV) introduced in the United
States and Europe has reduced the incidences of invasive pneumococcal
disease and AOM (
8,
13,
17,
25,
26). Nasopharyngeal carriage
and transmission in children were also reduced (
24). However,
in Japan, use of the 7-valent PCV has not yet been licensed,
and little is known about the distribution of pneumococcal serotypes.
Prior to the introduction of 7-valent PCV in Japan, it is important
to determine the distribution of pneumococcal serotypes in Japan
as well as the prevalence of antimicrobial-resistant pneumococci
associated with AOM. In this study, we evaluated the distribution
of pneumococcal serotypes among children with AOM and determined
the serotype coverage of pneumococcal vaccine formulas in Japan.
(This paper was presented at the 108th General Meeting of the American Society for Microbiology, Boston, MA, 1 to 5 June 2008.)
One hundred seventy-five pneumococcal isolates were collected randomly from middle ear fluids of 175 children with AOM at outpatient clinics in different regions of Japan during nationwide surveillance from February 2006 to June 2007. The range and quartiles of the ages of the subjects were 1 to 127, 12.8 (25th percentile), 17.0 (median), and 42.3 (75th percentile) months. Susceptibilities to penicillin G (PCG) were tested, and breakpoints were defined according to the Clinical and Laboratory Standards Institute (CLSI) (6). All isolates were serotyped or serogrouped by the capsular quelling method with pneumococcal capsule-specific antisera (Statens Serum Institut, Copenhagen, Denmark) as recommended by the manufacturer. The chi-square test and Fisher's exact test were used for categorical variables to test for significant differences between groups with Prism 4 (GraphPad Software, Inc.). A P value of <0.05 was considered statistically significant.
Out of 175 pneumococcal isolates, 63 (36.0%), 66 (37.7%), and 46 (26.3%) were penicillin-susceptible S. pneumoniae (PSSP), penicillin-intermediate-resistant S. pneumoniae (PISP), and PRSP, respectively (Table 1). The predominant serotype was 19F (19.4%), followed by 23F (14.9%), 14 (11.4%), 6B (11.4%), 6A (9.1%), and 3 (9.1%). The distribution of S. pneumoniae serotypes among PCG-susceptible strains was significantly different from that among PCG-resistant strains (P < 0.01). Serotype 3 was the most prevalent PSSP serotype (odds ratio [OR], 78.2; 95% confidence interval [CI], 4.6 to 1,330; P < 0.01), while serotype 19F (OR, 55.8; 95% CI, 3.4 to 929; P < 0.01) and serotype 23F (OR, 17.8; 95% CI, 2.4 to 135.1; P < 0.01) were frequently identified as drug-resistant S. pneumoniae (both PRSP and PISP). The proportions of serotypes 6A, 6B, and 14 were not different for PCG-susceptible and PCG-resistant isolates. The five predominant serotypes (19F, 23F, 6B, 6A, and 14) represented about 95.7% of the strains identified as PRSP. On the basis of age, PRSP strains were identified in 31.8% of children
2 years old, while PSSP strains were identified in 50.0% of children
3 years old. Serotypes 6A, 6B, 19F, and 23F were prevalent in children
2 years old, while serotype 3 was frequently identified in children
3 years old.
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TABLE 1. Serotype distribution and penicillin resistance of S. pneumoniae isolates from middle ear fluids of Japanese pediatric patients with AOM, based on age
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The total percentages (95% CIs) of serotypes covered by the
7-valent, 10-valent, 13-valent, and 23-valent pneumococcal vaccines
were 60.6 (53.3 to 68.7), 61.7 (54.5 to 68.9), 82.9 (77.3 to
88.4), and 73.7 (67.2 to 80.2), respectively (Table
2). The
percentages (95% CIs) of serotypes identified as PRSP and covered
by the 7-valent, 10-valent, 13-valent, and 23-valent pneumococcal
vaccines were 87.0 (77.2 to 96.7), 87.0 (77.2 to 96.7), 95.7
(89.8 to 100), and 87.0 (77.2 to 96.7), respectively. Among
children

2 years old, the total percentages (95% CIs) of serotypes
covered by the 7-valent, 10-valent, 13-valent, and 23-valent
pneumococcal vaccines were 68.2 (59.4 to 77.0), 69.2 (60.4 to
77.9), 86.0 (79.4 to 92.6), and 72.9 (64.5 to 81.3), respectively.
Among these same children, the percentages (95% CIs) of serotypes
identified as PRSP and covered by the 7-valent, 10-valent, 13-valent,
and 23-valent pneumococcal vaccines were 88.2 (77.4 to 99.1),
88.2 (77.4 to 99.1), 97.1 (91.4 to 100), and 88.2 (77.4 to 99.1),
respectively (Table
2). Among children

3 years old, the total
percentages (95% CIs) of serotypes covered by the 7-valent,
10-valent, 13-valent, and 23-valent pneumococcal vaccines were
48.5 (36.7 to 60.4), 50.0 (38.1 to 61.9), 77.9 (68.1 to 87.8),
and 75.0 (64.7 to 85.3), respectively. Among these same children,
the percentages (95% CIs) of serotypes identified as PRSP and
covered by the 7-valent, 10-valent, 13-valent, and 23-valent
pneumococcal vaccines were 83.3 (62.2 to 100), 83.3 (62.2 to
100), 91.7 (76.0 to 100), and 83.3 (62.2 to 100), respectively
(Table
2).
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TABLE 2. Serotype coverage of pneumococcal vaccines among Japanese pediatric patients with AOM, based on age and penicillin susceptibility
|
Currently available pneumococcal vaccines are designed to elicit
antibodies to the capsular polysaccharides of the most common
pneumococcal serotypes. Serotyping of pneumococcal isolates
from patients is an important tool for monitoring the effectiveness
of pneumococcal vaccines (
4,
8,
14). However, there are a limited
number of clinical trials, and the precise distribution of serotypes
among children with AOM in Japan still remains unclear (
1,
5).
Extreme diversity of distribution in pneumococcal serotypes
is a common phenomenon and is of great concern for researchers
in this field. As documented in previous reports, penicillin-resistant
strains were frequently identified among children

3 years old
(
11). The serotype distributions among Japanese children with
AOM were similar to those reported for children from the United
States and Europe (
2,
10,
15,
18). While the 7-valent PCV has
demonstrated its efficacy in the United States and Europe, the
formulation of a vaccine based on the existing data from the
United States and from European countries may not be optimal
for some Asian countries, because the distributions of
S. pneumoniae serotypes differ among nations (
8,
17,
25,
26). The 7-valent
PCV covers most of the strains of PRSP found in Japanese children,
especially those <3 years old. These findings have implications
for the potential use of the 7-valent PCV in Japan. Serotype
6C was recently discovered among serotype A pneumococcal strains
(
19,
20). Consequently, the cross-protection provided against
serotype 6C by the currently available pneumococcal vaccine
containing antibodies against 6B may be inadequate, and the
vaccine may reduce the prevalence of serotype 6A but not serotype
6C (
19,
20). We must therefore pay attention to the prevalence
of serogroup 6 before and after the introduction of 7-valent
PCV. The shift in serotype replacement over time also may eventually
make a given vaccine formulation obsolete. Several studies have
reported a change in serotype after vaccination, with the increases
in serotypes 3, 6A, 19A, and 23A being of particular concern
(
16,
22-
23). Serotype 19A emerged as the most frequent cause
of invasive pneumococcal disease in the United States after
the introduction of the 7-valent PCV (
22). In Japan, where the
7-valent PCV has not yet been licensed, the prevalence of the
serotype 19A strain is currently low. Continuous surveillance
is necessary to monitor the distribution of antimicrobial-resistant
pneumococci and their serotypes before and after the introduction
of the 7-valent PCV.

ACKNOWLEDGMENTS
We greatly thank all of the members of ATOMS for collecting
middle ear fluids and Yuki Tatsumi (Department of Otolaryngology,
Head and Neck Surgery, Wakayama Medical University, Wakayama,
Japan) for her technical assistance.
This work was supported by national grants from the Japanese Ministry of Education, Culture, Sports, Science and Technology (no.19591987 and 19791224).
We have no conflicts of interest.

FOOTNOTES
* Corresponding author. Mailing address: Department of Otolaryngology, Head and Neck Surgery, Wakayama Medical University, 811-1 Kimiidera, Wakayama-shi, Wakayama 640-8501, Japan. Phone: 81-73-441-0651. Fax: 81-73-446-3846. E-mail:
ynobi{at}wakayama-med.ac.jp 
Published ahead of print on 1 October 2008. 

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Journal of Clinical Microbiology, November 2008, p. 3808-3810, Vol. 46, No. 11
0095-1137/08/$08.00+0 doi:10.1128/JCM.01782-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.