Changes over 10 years of ampicillin-resistant Haemophilus influenzae isolated from children

Abstract

We examined the frequency of ampicillin (ABPC) resistance of 3784 strains of Haemophilus influenzae isolated from the infants aged from 1 month after birth to 12 years who had been treated in the Pediatric Department of our hospital for 9 years and 6 months from July 1999 to December 2008. We determined the drug susceptibility by Etest, and judged the resistance by the standard of Clinical and Laboratory Standard Institute. The rate of strains of MIC of less than 2𝜇g/ml to ABPC was 87.1% in 1999, but the ratio was decreasing year after year significantly up to 28.7% in 2008 (p<0.001). 𝛽-lactamase negative ABPC resistant (BLNAR) strains whose MIC to ABPC was more than 4𝜇g/ml was 2.9% in 1999, but increased significantly to 43.3% in 2008 (p<0.001). MIC₉₀ was 2𝜇g/ml in 1999, but increased to 16𝜇g/ml in 2008.