Invasive Haemophilus influenzae type b disease in England and Wales: who is at risk after 2 decades of routine childhood vaccination?

BACKGROUND: The introduction of the Haemophilus influenzae serotype b (Hib) conjugate vaccine into national immunization has led to rapid and sustained declines in invasive Hib disease incidence across all age groups. In industrialized countries with established Hib vaccination programs, however, little is known about individuals who develop invasive Hib disease. This study describes the epidemiology of invasive Hib disease in England and Wales during 2000-2012 and the clinical characteristics of laboratory-confirmed Hib cases diagnosed during 2009-2012.

METHODS: Public Health England (PHE) conducts enhanced national surveillance of invasive Hib disease in England and Wales. Detailed clinical information was obtained for all laboratory-confirmed Hib cases diagnosed during 2009-2012.

RESULTS: Invasive Hib disease in England and Wales has been declining since 2002, reaching its lowest incidence of 0.02 per 100 000 (14 cases) in 2012. In children aged <5 years of age, Hib incidence was 0.06 per 100 000 (2 cases), compared with 35.5 per 100 000 prior to routine Hib vaccination. Follow-up of all 106 case patients over the 4-year period revealed that most cases occurred in adults (73%) who often had preexisting medical conditions (77%) and presented with pneumonia (56%). The Hib-associated case fatality rate was 9.4% (10/106 cases).

CONCLUSIONS: Control of Hib disease in England and Wales is currently the best that has been achieved since the introduction of routine Hib vaccination in 1992. Invasive Hib disease is no longer a major cause of acute bacterial meningitis in children but, instead, cases are more likely to present as pneumonia in older adults with comorbidities, similar to the less virulent nonencapsulated H. influenzae.