Epidemiology of Haemophilus influenzae bacteremia: A multi-national population-based assessment

Summary Objectives Haemophilus influenzae is an important cause of invasive infection but contemporary data in non-selected populations is limited. Methods Population-based surveillance for Haemophilus influenzae bacteremia was conducted in seven regions in Australia, Canada, and Denmark during 2000–2008. Results The overall annual incidence rate was 1.31 per 100,000 population and type specific rates were 0.08 for H. influenzae serotype b (Hib), 0.22 for H. influenzae serotypes a, c-f (Hiac-f), and 0.98 per 100,000 for non-typeable H. influenzae (NTHi). Very young and old patients were at highest risk. The serotypes causing disease varied according to age with nearly all cases in the elderly due to NTHi. The presence of comorbid medical illness was common with 14%, 16%, and 29% patients having Charlson comorbidity scores of 1, 2, and ≥3, respectively. The 30-day all-cause case-fatality rate was 18%. Factors independently associated with death at 30-days in logistic regression analysis included male gender, hospital-onset disease, older age, and lower respiratory tract, central nervous system, or unknown focus of infection. Conclusions Haemophilus influenzae is an important cause of morbidity and mortality particularly with NTHi in the elderly. These data serve as a baseline to assess the future effectiveness of new preventative interventions.