[Bacteriological Analysis of Pneumococcus Detected from the Sputum of Hospitalized Children]

7-valent pneumococcal conjugate vaccine (PCV7) has been included in the routine immunization schedule since April 2013 in Japan. Serotype replacement - a phenomenon by which serotypes are replaced by non-vaccine serotypes after vaccine introduction - has been reported in invasive pneumococcal disease (IPD). Pneumococcus in sputum samples is one of the major causes of bronchopulmonary infection in children. We tried to verify whether serotype replacement of Pneumococcus occurs in sputum samples in a similar manner as in IPD. From August 2014 to September 2015, we performed antimicrobial susceptibility testing and serotyping of Streptococcus pneumoniae from sputum samples and investigated the history of PCV from hospitalized children with S. pneumoniae bronchopulmonary infection. From the results of our investigation, 80.3% of children have received PCV at least once. Serotypes of Pneumococcus were determined in 92.4% of tested strains and PCV13 strains accounted for only 9.8%. Major isolated serotypes were 15A (21.3%), 35B (19.7%), and 6C (13.1%). Those were not included in PCV13, i.e. serotype replacement occurs in bronchopulmonary infection just as in IPD. The results of antimicrobial susceptibility testing for Penicillin G indicated that penicillin-resistant S. pneumoniae (PRSP) accounted for 4.5%, penicillin-intermediate resistant S. pneumoniae (PISP) accounted for 47.0% and penicillin-susceptible S. pneumoniae (PSSP) accounted for 48.5%. When examining the drug susceptibility by serotypes, 15A, 19A, 23A and 35B showed a high percentage of non-susceptibility. This means there is a difference in the resistant trend by serotypes. In our study, it became clear that verifying of the serotypes of Pneumococcus in sputum is meaningful and surveillance of serotypes is important for evaluation of vaccination as IPD.