Increasing Incidence of Invasive Haemophilus influenzae Disease in Adults, Utah, USA

Since the introduction of the Haemophilus influenzae type b vaccine, the incidence of invasive H. influenzae type b disease among children has fallen dramatically, but the effect on invasive H. influenzae disease among adults may be more complex. In this population-based study we examined the epidemiology and outcomes of invasive disease caused by typeable and nontypeable H. influenzae among Utah adults during 1998-2008. The overall incidence increased over the study period from 0.14/100,000 person-years in 1998 to 1.61/100,000 person-years in 2008. The average incidence in persons >= 65 years old was 2.74/100,000 person-years, accounting for 51% of cases and 67% of deaths. The incidence was highest for nontypeable H. influenzae (0.23/100,000 person-years), followed by H. influenzae type f (0.14/100,000 person-years). The case-fatality rate was 22%. The incidence of invasive H. influenzae infection in Utah adults appears to be increasing. Invasive H. influenzae disproportionately affected the elderly and was associated with a high mortality rate.