Population genetics and antibiotic susceptibility of invasive Haemophilus influenzae in Manitoba, Canada, from 2000 to 2006.

One hundred and twenty-two isolates of Haemophilus influenzae causing invasive disease were collected in Manitoba, Canada, from 2000 to 2006 and examined for serotype, biotype, sequence type (ST) by multilocus sequence typing and antibiotic susceptibility. Nonserotypeable (NST) isolates accounted for over half of the isolates collected (69 isolates, 56.6%). There were 36 serotype a, five serotype b, two serotype c, one serotype d, four serotype e and five serotype f isolates collected. The 69 NST isolates were found to be very diverse, with isolates representing six biotypes and 45 STs. The serotypeable isolates were more clonal, with each of the serotypes showing little diversity in their biotypes and STs. Of the 122 isolates, 17% were resistant to ampicillin due to beta-lactamase production, 10.7% were resistant to trimethoprim-sulfamethoxazole, 1.6% were resistant to clarithromycin, 2.5% were resistant to amoxicillin-clavulanic acid and none was resistant to ciprofloxacin or moxifloxacin. Antibiotic resistance was more common in the NST strains, with 37.7% showing resistance to at least one antibiotic compared to 15% in the serotypeable strains. The results of this study suggest a shift in the epidemiology of invasive H. influenzae infections in the post-Hib vaccine era, and surveillance should include all serotypeable and NST isolates.