In countries with established Haemophilus influenzae type b (Hib) immunization programs, nontypeable H. influenzae (NTHi) is now responsible for nearly all invasive H. influenzae cases across all age groups.
Public Health England (PHE) conducts enhanced national surveillance of invasive H. influenzae disease in England and Wales. Invasive NTHi isolates submitted to Public Health England from children of ages 1 month to 10 years during 2003–2010 were characterized by multilocus sequence typing (MLST). Detailed clinical information was obtained for all laboratory-confirmed cases of invasive NTHi disease in children during 2009–2013.
In England and Wales, there were 7797 cases of invasive H. influenzae disease diagnosed during 2000–2013 and 1585 (20%) occurred in children aged 1 month to 10 years, where NTHi was responsible for 31–51 cases (incidence, 0.53–0.92/100,000) annually. Detailed clinical follow-up of 214 confirmed NTHi cases diagnosed in this age-group during 2009–2013 revealed that 52% (n = 111) occurred in <2-year-old and 52% (n=110) had comorbidity. Bacteremic pneumonia was the most common clinical presentation (n = 99, 46%), 16% (n = 34) required intensive care and 11% (n = 23) died. Characterization by biotyping and MLST of 316 NTHi strains from children with invasive disease during 2003–2010 revealed a genetically heterogeneous population (155 MLSTs) with diverse biotypes and no association with comorbidity status, clinical disease or outcome.
The high level of genetic diversity in invasive NTHi strains highlights the difficulties in developing an effective vaccine against this pathogen.