Changes in the Serotype Distribution among Antibiotic Resistant Carriage Streptococcus pneumoniae Isolates in Children after the Introduction of the Extended-Valency Pneumococcal Conjugate Vaccine

BACKGROUND: The aim of this study is to investigate the serotype distribution and antimicrobial resistance of nasopharyngeal isolates of Streptococcus pneumoniae from children after the introduction of the extended-valency pneumococcal conjugate vaccines (PCVs) in Korea. METHODS: From July 2010 to June 2015, 3,820 nasopharyngeal aspirates obtained from infants and children who presented with respiratory symptoms at the Seoul National University Children’s Hospital were plated on trypticase soy agar containing 5% sheep blood for isolation of pneumococci. Serotype was determined by Quellung reaction and antimicrobial susceptibility was tested by E-test. Trend analysis was performed for serotype distribution and antimicrobial non-susceptibility rates. RESULTS: S. pneumoniae was isolated from 397 (10.4%) specimens. The most common serotypes were 19A (14.0%), 23A (12.8%), 15B/C (10.7%), 11A (10.1%), 6C (7.8%), and 6A (6.3%) among the typeable pneumococci (n = 335). The PCV serotype proportions significantly decreased (59.1% in 2010/11 to 17.0% in 2014/15, P < 0.001), whereas the non-PCV serotype proportions significantly increased (40.9% in 2010/11 to 83.0% in 2014/15, P < 0.001). The non-susceptibility rates for penicillin (oral), penicillin (parenteral, non-meningitis), cefotaxime, and erythromycin were 97.8%, 22.8%, 27.7%, and 95.5%, respectively. The proportions of PCV serotypes responsible for non-susceptibility to penicillin (parenteral, non-meningitis) and multidrug resistance significantly decreased (80.8% to 21.1%, P < 0.001, 64.3% to 12.3%, P < 0.001, respectively), whereas the non-PCV serotype proportions significantly increased (19.2% to 78.9%, P < 0.001, 35.7% to 87.7%, P < 0.001, respectively). Serotypes 23A and 15B/C demonstrated significant proportional increase among the antibiotics resistant strains. CONCLUSION: The PCV serotype proportions decreased and the non-PCV serotype proportions increased among nasopharyngeal carriage pneumococci after the introduction of extended-valency PCVs in Korea. Antimicrobial non-susceptibility rates for penicillin and erythromycin remain high despite the decrease in the proportion of PCV serotypes responsible for antimicrobial resistance over time. DISCLOSURES: All authors: No reported disclosures.