Genetic Structures of Streptococcus pneumoniae Invasive Isolates from Korean Children Obtained Between 1995 and 2013

Abstract

Background. Understanding the population genetics of pneumococci will allow detection of changes in the prevalence of circulating genotypes and evidence for capsular switching after the use of pneumococcal conjugate vaccines (PCVs). We aimed to analyze the genetic structure of invasive pneumococcal isolates obtained from children before and after the optional use of PCV7 and PCV10/13 in Korea. Methods. A total of 285 invasive pneumococcal isolates obtained from children aged <18 years in multicenters during 1995-2013 were included. We classified the isolation year to pre-PCV7 (1995-2003; n = 70), post-PCV7 (2004-2010; n = 142), and post-PCV13 (2011-2013; n = 73) periods. Isolates were analyzed using serotyping, multilocus sequence typing, and antimicrobial susceptibility testing. Results. Between pre-PCV7 and post-PCV13 periods, PCV7 serotypes decreased significantly (from 67.1% to 9.6%, P < 0.001) whereas non-vaccine serotypes (NVTs) showed a significant increase (from 2.9% to 53.9%, P < 0.001). Of the 10 clonal complexes (CCs), antibiotic-resistant international clones, CC320 (31.6%), CC81 (14.7%), and CC166 (6.7%) were the main complexes. Serotype 19A was the main serotype of CC320 throughout the periods. Serotype of CC81 mainly comprised of 23F (53.3%) in pre-PCV7 period and replaced by non-vaccine types (NVTs; 6C [10%], 13 [30%], 15A [40%], and 15B/C [20%]) in post-PCV13 period. The main serotype responsible for CC166 also changed from 9V (80%) in pre-PCV7 to NVT 11A (50%) in post-PCV13 periods. Non-susceptibility to penicillin (42.3%) was the highest in CC320, increasing from 0% to 76%. Conclusion. Genetic structure of IPD isolates in Korean children has changed after the PCV7 and PCV10/13 implementations, and the genotypes of PCV7 types during pre-PCV7 period were mostly disappeared and re-occupied by genotypes of PCV13 types/NVTs in post-PCV13 period. Serotype 19A/ST320 were expected to decrease rapidly after the use of PCV13 in national immunization program.