[Colonization and transmission of Haemophilus influenzae type b (Hib)]

Haemophilus influenzae type b (Hib) remains the leading cause of invasive bacterial infection in Japanese children. More than 110 countries that have included Hib conjugate vaccines in their routine vaccination programs have seen dramatical decrease in the incidence of Hib infections. In Japan, the vaccine has been introduced for voluntary immunization since December 2008 and has been provided free of charge only since January 2011. This review reports the prevalence of Hib and its clones among healthy children and pediatric patients diagnosed with invasive or non-invasive Hib infections in Sado Island, Japan. Of 25 Hib isolates collected in this surveillance, 4 genotypic patterns (ST54-gBLPACR-III, ST54-gBLNAR-I/II, ST190-gBLNAS, and ST95-gBLPACR-I/II) were detected. These STs were double or triple-locus variants of each other. Under the same antimicrobial selective pressure, high prevalence of gBLPACR strain (76.0%) was confirmed in Hib isolates, while gBLPACR prevalence in nontypeable H. influenzae was very low (5.2%). These data suggested that each ST strain may be brought into Sado Island by different routes. We note that surveillance of healthy subjects to identify Hib carriers is important to understand their role in transmission of Hib.