Abstract
Moraxella catarrhalis is present in the upper respiratory tract often together with Streptococcus pneumoniae and Haemophilus influenzae and it causes sinusitis, tympanitis and other respiratory ailments. The national vaccination program in Japan against S. pneumoniae and H. influenzae was revised in 2010 so that children less than 5 years of age are eligible for vaccination. It is, therefore, potentially conceivable that the isolation frequencies of these pathogens may have varied thereafter. We conducted a survey of the occurrence of M. catarrhalis for six consecutive years from 2009 to 2014 at Kitasato University Hospital. The isolation frequency of M. catarrhalis from 2009 to 2014 increased consistently with age. This trend was markedly significant in children up to 5 years of age, suggesting a possibility that the vaccination program affected the populations of these pathogens. Among M. catarrhalis isolates, the MIC90 of levofloxacin-resistant strains increased 2-fold in children less than 5 years of age and 4-fold in adults more than 65 years of age in 2013. We interpreted the data to mean that the levofloxacin-resistant strains had been transmitted from elderly carriers to these children, because new quinolone antibiotics are not prescribed to children less than 5 years of age in general.
