High prevalence of nasal carriage of β-lactamase-negative ampicillin-resistant Haemophilus influenzae in healthy children in Korea

This study investigated the carriage of antimicrobial resistant Haemophilus influenzae in 582 healthy children attending kindergarten or elementary school at four intervals over a 9-month period in Seoul, Korea. Diverse colonization patterns and a lower level of long-term persistent carriage by H. influenzae status were evident in this study. Colonizing H. influenzae isolates showed a high rate of resistance to beta-lactams including ampicillin (51.9%), cefaclor (52.1%), and amoxicillin/clavulanate (16.3%). Based on the ampicillin resistance mechanism, H. influenzae isolates were categorized as beta-lactamase-negative, ampicillin-susceptible (BLNAS) (48.1%), beta-lactamase-positive, ampicillin-resistant (BLPAR) (22.6%), beta-lactamase-negative, ampicillin-resistant (BLNAR) (22.8%), and beta-lactamase-positive, amoxicillin/clavulanateresistant (BLPACR) strains (6.5%). This study provides the first evidence of a high prevalence (22.8%) of BLNAR strains of H. influenzae nasal carriage in healthy children attending kindergarten or the first 2 years of elementary school in Korea. The high carriage of these resistant strains in overcrowded urban settings may create reservoirs for development of H. influenzae-resistant strains.