Invasive Streptococcus pneumoniae infections in children in Kamikawa and Soya subprefecture, Hokkaido, Japan, 2000–2010, before the introduction of the 7-valent pneumococcal conjugate vaccine

We evaluated 103 cases of invasive pneumococcal disease (IPD) encountered in 99 children (two developed the disease twice and one, three times) treated in the northern district of Hokkaido (Kamikawa and Soya subprefecture) from April 2000 until March 2010, before the introduction of the 7-valent pneumococcal conjugate vaccine. The main diseases were as follows: pneumonia, 54 cases (52.9%); occult bacteremia, 34 cases (33.3%); meningitis, five cases (4.9%). There were 42 cases during the first half of the study period (from April 2000 to March 2005) and 61 during the second half (from April 2005 to March 2010). The IPD morbidity rate for the 10-year period was 41.3 per 100,000 population in children <5 years and 79.2 per 100,000 population in children <2 years. Serotype analysis of the 77 strains was performed. The most frequent serotype isolated was 6B (31.2%), followed by 23F (14.3%), 19F (13.0%), 9V (7.8%), 6A (7.8%), and 14 (3.9%). The number of strains that could potentially be covered by heptavalent pneumococcal conjugate vaccine was 55 (71.4%), and the number of strains that could potentially be covered by 13-valent pneumococcal conjugate vaccine was 64 (83.1%). Analysis of penicillin-binding protein (PBP) genes was performed of the 82 strains. The percentages of resistant bacteria caused by PBP gene mutations were 42.7% (35 strains) for gPRSP, 48.8% for gPISP (40 strains), and 8.5% for gPSSP (7 strains).