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.
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.
TABLE 1.
Serotype distribution and penicillin resistance of S. pneumoniae isolates from middle ear fluids of Japanese pediatric patients with AOM, based on age
| Serotype | No. (%) of isolates from indicated age group
|
|||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ≤2 yr
|
≥3 yr
|
All
|
||||||||||
| PSSP | PISP | PRSP | Total | PSSP | PISP | PRSP | Total | PSSP | PISP | PRSP | Total | |
| 1 | 1 (1.5) | 1 (1.5) | 1 (0.6) | 1 (0.6) | ||||||||
| 3 | 3 (2.8) | 3 (2.8) | 13 (19.1) | 13 (19.1) | 16 (9.1) | 16 (9.1) | ||||||
| 4 | 1 (1.5) | 1 (1.5) | 1 (0.6) | 1 (0.6) | ||||||||
| 6A | 5 (4.7) | 6 (5.6) | 3 (2.8) | 14 (13.1) | 1 (1.5) | 1 (1.5) | 2 (2.9) | 6 (3.4) | 6 (3.4) | 4 (2.3) | 16 (9.1) | |
| 6B | 7 (6.5) | 9 (8.4) | 3 (2.8) | 19 (17.8) | 1 (1.5) | 1 (1.5) | 8 (4.6) | 9 (5.1) | 3 (1.7) | 20 (11.4) | ||
| 7F | 1 (0.9) | 1 (0.9) | 1 (0.6) | 1 (0.6) | ||||||||
| 9V | 2 (2.9) | 2 (2.9) | 2 (1.1) | 2 (1.1) | ||||||||
| 9N | 1 (0.9) | 1 (0.9) | 1 (0.6) | 1 (0.6) | ||||||||
| 10A | 3 (2.8) | 3 (2.8) | 3 (4.4) | 3 (4.4) | 6 (3.4) | 6 (3.4) | ||||||
| 11A | 1 (0.9) | 1 (0.9) | 1 (1.5) | 1 (1.5) | 2 (1.1) | 2 (1.1) | ||||||
| 12F | 1 (0.9) | 1 (0.9) | 1 (1.5) | 1 (1.5) | 2 (1.1) | 2 (1.1) | ||||||
| 14 | 1 (0.9) | 7 (6.5) | 2 (1.9) | 10 (9.3) | 3 (4.4) | 6 (8.8) | 1 (1.5) | 10 (14.7) | 4 (2.3) | 13 (7.4) | 3 (1.7) | 20 (11.4) |
| 15B | 2 (1.9) | 2 (1.9) | 1 (1.5) | 1 (1.5) | 2 (2.9) | 1 (0.6) | 3 (1.7) | 4 (2.3) | ||||
| 18C | 2 (1.9) | 2 (1.9) | 1 (1.5) | 1 (1.5) | 3 (1.7) | 3 (1.7) | ||||||
| 19A | 1 (0.9) | 1 (0.9) | 4 (5.9) | 4 (5.9) | 5 (2.9) | 5 (2.9) | ||||||
| 19F | 11 (10.3) | 13 (12.1) | 24 (22.4) | 4 (5.9) | 6 (8.8) | 10 (14.7) | 15 (8.6) | 19 (10.9) | 34 (19.4) | |||
| 22F | 1 (1.5) | 1 (1.5) | 1 (0.6) | 1 (0.6) | ||||||||
| 23F | 1 (0.9) | 5 (4.7) | 12 (11.2) | 18 (16.8) | 5 (7.4) | 3 (4.4) | 8 (11.8) | 1 (0.6) | 10 (5.7) | 15 (8.6) | 26 (14.9) | |
| Group 23 | 2 (1.9) | 1 (0.9) | 3 (2.8) | 3 (4.4) | 3 (4.4) | 5 (2.9) | 1 (0.6) | 6 (3.4) | ||||
| non23 | 2 (1.9) | 2 (1.9) | 4 (3.7) | 1 (1.5) | 2 (2.9) | 1 (1.5) | 4 (5.9) | 3 (1.7) | 4 (2.3) | 1 (0.6) | 8 (4.6) | |
| Total | 29 (27.1) | 44 (41.1) | 34 (31.8) | 107 (100) | 34 (50.0) | 22 (32.4) | 12 (17.6) | 68 (100) | 63 (31.2) | 66 (32.7) | 46 (22.8) | 175 (100) |
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).
TABLE 2.
Serotype coverage of pneumococcal vaccines among Japanese pediatric patients with AOM, based on age and penicillin susceptibility
| Vaccine type (established formula) | No. (%) of isolates from indicated age group
|
|||||
|---|---|---|---|---|---|---|
| ≤2 yr
|
≥3 yr
|
All
|
||||
| PRSP (n = 34) | Total (n = 107) | PRSP (n = 12) | Total (n = 68) | PRSP (n = 46) | Total (n = 175) | |
| 7-Valent (4, 6B, 9V, 14, 18C, 19F, 23F) | 30 (88.2) | 73 (68.2) | 10 (83.3) | 33 (48.5) | 40 (87.0) | 106 (60.6) |
| 10-Valent (1, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, 23F) | 30 (88.2) | 74 (69.2) | 10 (83.3) | 34 (50.0) | 40 (87.0) | 108 (61.7) |
| 13-Valent (1, 3, 4, 5, 6A, 6B, 7F, 9V, 14, 18C, 19A, 19F, 23F) | 33 (97.1) | 92 (86.0) | 11 (91.7) | 53 (77.9) | 44 (95.7) | 145 (82.9) |
| 23-Valent (1, 3, 4, 5, 6B, 7F, 8, 9V, 9N, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 22F, 23F, 33F) | 30 (88.2) | 78 (72.9) | 10 (83.3) | 51 (75.0) | 40 (87.0) | 129 (73.7) |
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
Published ahead of print on 1 October 2008.
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