Trends in antimicrobial susceptibility of Streptococcus pneumoniae in the Tohoku district of Japan: A longitudinal analysis from 1998 to 2007

Streptococcus pneumoniae is a common cause of respiratory tract infections (RTI5). The prevalence of Streptococcus pneumoniae strains with reduced susceptibility to antimicrobial agents has dramatically increased worldwide. Susceptibility to nine antimicrobial agents and serotypes were determined among 1,644 Streptococcus pneumoniae strains isolated from patients with RTI5 in the Tohoku district of Japan from October to December every year from 1998 to 2007. The prevalence of penicillin G-nonsusceptible Streptococcus pneumoniae (PNSP) strains increased gradually from 48.5% in 1998, reached a statistical peak in 2004 (65.1%) and then decreased to 51.5% in 2007. Streptococcus pneumoniae strains with each serotype 3, 6, 19 and 23 were constantly detected, and the distribution of these serotypes in PNSP strains did not significantly change during the study period. A trend of Streptococcus pneumoniae strains nonsusceptible to other β-lactams tested was similar to that of PNSP strains, except for cefditoren, to which the resistance rate was <20% throughout the analysis period. The prevalence of strains nonsusceptible to erythromycin and minocycline were consistently >60%. Almost all penicillin G-resistant Streptococcus pneumoniae (PRSP) strains were resistant to both erythromycin and minocycline throughout the analysis period. The prevalence of strains resistant to fluoroquinolones tested were <3% over the study period. Our longitudinal surveillance demonstrated for the first time that decreased prevalence of both βlactam- and multidrug-resistant strains has been occurring since 2004 in a region of Japan. Careful monitoring of antimicrobial susceptibility of Streptococcus pneumoniae should be continued.