Changes in the Distribution of Capsular Serotypes of Streptococcus pneumoniae Isolated from Adult Respiratory Specimens in Japan

Objective The objective of this study was to assess whether the distribution of pneumococcal capsular types has been changed, while also providing basic data on changes in the distribution after the introduction of Pneumococcal conjugated vaccine (PCV)13 in adult medical practice. Methods We analyzed 431 Streptococcus pneumoniae strains (200 in 2006 and 231 in 2012) that had been isolated from respiratory infection specimens from adult patients. Capsular typing was performed by the Quellung reaction and multiplex polymerase chain reaction. Results A comparison of the 2006 and 2012 strains revealed that the number and proportion of strains by serotype increased from 30 (15%) to 46 (20%) for serotype 3, from 4 (2%) to 14 (6%) for serotype 6A, and from 4 (2%) to 13 (6%) for serotype 6C, whereas the number and proportion of strains by serotype decreased from 8 (4%) to 0 (0%) for serotype 4 and from 24 (12%) to 17 (7%) for serotype 6B. From 2006 to 2012, the coverage rate significantly decreased from 39 to 28.1% for PCV7 (p=0.017). Conclusion Our study showed a decrease in the vaccine coverage of PCV7. However, PCV13 covered serotypes 3 and 6A, which are prevalent, as well as penicillin-resistant S. pneumoniae strains. At present, PCV13 in adult clinical practice seems to be highly significant. However, there is a possibility that the distribution has changed, and careful screening should be continued in the future.