Serotype and Antibiotic Resistance of Streptococcus pneumoniae Isolates from Invasive Disease in Children after Optional Use of the 7-valent Conjugate Vaccine

Abstract

Introduction: Streptococcus pneumoniae is a major cause of invasive bacterial infections in children. Serotype distribution of pneumococcus is different according to the study period and region, and it is also influenced by type of vaccine used. The purpose of this study is to investigate serotype distribution and antimicrobial susceptibility of pneumococcal isolates from invasive infections in children by a multicenter study, between 2006 and 2010, when 7-valent pneumococcal conjugate vaccine (PCV7) had been widely used and 10 (PCV10) or 13-valent (PCV13) vaccine has just been introduced in Korea. Methods: From January 2006 to December 2010, 140 pneumococcal isolates from invasive infections in children younger than 18 years collected in 8 centers in Korea were included in this study. Serotype was determined by Quellung reaction or multiplex polymerase chain reaction. Antimicrobial susceptibility was tested by E-test and interpreted according to the 2003 CLSI guideline for epidemiological comparison. Medical records of the patients were reviewed retrospectively. Results: The most common serotypes among 140 isolates were 19A (n=32, 22.9%), 19F (n=17, 12.1%), 6B (n=12, 8.6%), and 23F (n=11, 7.9%). Overall, the proportions of PCV7 serotypes were 45.0%, additional 3 serotypes in PCV10 were 2.9%, and 3 PCV13-specific serotypes were 29.3%. In a trend analysis of yearly serotype proportion between 2006 and 2010, PCV7 serotype had decreased from 62.5% to 21.4% (P=0.002), whereas additional 6 serotypes in PCV13 had increased from 21.9% to 46.4% (P=0.031). Antimicrobial susceptibility test was done for 123 isolates, nonsusceptibility rates of penicillin, cefotaxime, and erythromycin were 88.6%, 23.6%, and 87.0%, respectively. Penicillin nonsusceptibility rates of PCV7 serotypes, additional 3 serotypes in PCV10, 3 PCV13-specific serotypes, and nonvaccine serotypes were 91.2%, 0.0%, 94.4%, and 85.2%

cefotaxime nonsusceptibility rates were 17.5%, 0.0%, 47.2%, and 7.4%

and erythromycin nonsusceptibility rates were 94.7%, 33.3%, 91.7%, and 70.4%, respectively. Conclusions: In this study of pneumococcal isolates from pediatric invasive infection between 2006 and 2010, the proportion of PCV7 serotypes decreased, while additional serotypes in PCV13 increased over time. Antimicrobial resistance rates were higher in PCV7 serotypes and additional serotypes in PCV13. These findings can be the basis of pneumococcal vaccine policy and treatment strategy of pneumococcal infections in children in Korea.