Prevalence of β-lactamase-nonproducing ampicillin-resistant Haemophilus influenzae and Haemophilus influenzae type b strains obtained from children with lower respiratory tract infections

The prevalence of strains with ampicillin (ABPC) resistance among Haemophilus influenzae strains isolated from the nasopharynx of children with lower respiratory tract infections has increased significantly during the 6 years from 2000, when it was 41.9%, to 2005, when it reached 60.1%. From 2002, the prevalence exceeded 50%, and the prevalence of β-lactamase-nonproducing ABPC-resistant (BLNAR) strains with a minimum inhibitory concentration (MIC) of ABPC of over 4 µg/ml doubled, from 28.2% in 2002 to 54.7% in 2005. In H. influenzae strains obtained from the nasopharynx of children with lower respiratory tract infections between April 2004 and March 2006, identification of serotype b was defined, using the slide agglutination method. The frequency of isolation of H. influenzae type b (Hib) strains was then measured and the ABPC resistance conditions of the Hib strains were also evaluated. The frequency of the Hib strains was found to be 30 out of 479 strains, 6.3%. Of these 30 strains, BLNAR accounted for 53.3% (16 strains), approximately the same frequency of isolation as that of the BLNAR isolated from all H. influenzae strains during the same period. In Japan, the prevalence of BLNAR strains among clinically isolated H. influenzae strains has continued to increase, and the frequency of isolation of BLNAR strains among Hib strains has also continued to rise. As a countermeasure, attempts at improving resistance have been made through judicious antibiotic use, but concern that the choice of antibiotics for Hib meningitis may become complicated has sparked a keen interest in the introduction of Hib conjugate vaccine.