2019 Volume 68 Issue 4 Pages 731-736
The pneumococcal conjugate vaccine (PCV) was introduced to the routine immunization schedule in 2013, and the serotype replacement of isolated Streptococcus pneumoniae strains has attracted attention. In this study, we surveyed the capsular serotypes of strains isolated from children and compared the results with those of two previous surveys conducted in 2002 and 2008. The materials were 184 Streptococcus pneumoniae isolates from 184 patients who visited the Pediatrics Department of our hospital during the 1-year period from August 2016 to July 2017. We determined 39 capsular serotypes by the slide agglutination method using an immune serum (“SEIKEN”, Denka Seiken Co., Ltd.), and we defined isolates that did not show agglutination as nontypable (NT). All PCV13-related serotypes could be determined by this method, but subtypes could not be assessed. The serotypes were in the following order: 92 NT isolates (50.0%), 25 type-15 isolates (13.6%), 18 type-35 isolates (9.8%), 11 type-11 isolates (6.0%), 8 type-22 isolates (4.3%), and 30 isolates of other types (16.3%). PCV13-related serotypes were found in only 14 isolates (7.6%). NT isolation rates (50.0%) showed a marked increase compared with those in 2002 (3.1%) and 2008 (5.1%). The decrease in isolation rate of PCV13-related serotypes from 83.9% in 2002 and 85.5% in 2008 to 7.6% in this survey suggests that serotype replacement had occurred following the introduction of PCV13.
