Invasive Haemophilus influenzae in British Columbia: non-Hib and non-typeable strains causing disease in children and adults

Summary Objectives To characterize invasive Haemophilus influenzae and to examine the population at risk for invasive H. influenzae disease in British Columbia, Canada, 2008–2009. Methods H. influenzae recovered from individual patients were characterized by serotyping, biotyping, multilocus sequence typing (MLST), and antibiotic susceptibility testing. Age information was recorded from specimen requisition forms. Results Of the 98 cases, 66% were caused by non-typeable strains, followed by serotypes b (12%), a (10%), f (10%), and e (1%). Cases caused by serotypes b and f and non-typeable strains were mainly in adults over 18 years of age, while cases due to serotype a were mainly in children under the age of 2 years. Different sequence types were found in encapsulated strains according to their serotypes, and non-typeable strains had their own unique sequence types. No capsule switching was documented. Antibiotic resistance was common among non-typeable strains, with 31% identified as genotypic β-lactamase-negative ampicillin-resistant (BLNAR) strains. Conclusion Invasive H. influenzae disease in a population vaccinated against Hib was age-dependent and involved both non-typeable and encapsulated strains. Adults were susceptible to invasive diseases due to non-typeable and serotype b and f strains, while in children, most diseases were due to serotype a bacteria.