Invasive Haemophilus influenzae disease in adults

We reviewed retrospectively all invasive Haemophilus influenzae (Hi) infect ions in adults ascertained from reference laboratory records and notificati ons from five NHS regions over the 5 years from 1 October 1990, a period en compassing the introduction of routine Hib childhood immunization (October 1992). A total of 446 cases were identified, a rate of 0.73 infections per 10(5) adults per annum, Though numbers of Hib infections in adults fell aft er the introduction of Hib vaccines for children (P = 0.035), and there was no increase in infections caused by other capsulated Hi serotypes, total n umbers of invasive Hi infections increased due to a large rise in infection s caused by non-capsulated Hi (ncHi) strains (P = 0.0067). There was an une xpectedly low rate of infections in those aged 75 years or more (P < 0.0001 ). The commonest clinical presentations were pneumonia with bacteraemia (22 7/350, 65%) and bacteraemia alone (62/350, 18%) and the highest rates of di sease were in the 65-74 years age group (P < 0.0001). Clinical presentation was not influenced by the capsulation status of the invading Hi strain. 10 3/350 cases (29%) died within 1 month, and 207/350 (59%) within 6 months of their I-Ii infection, Case fatality rates were high in all age groups. Pre -existing diseases were noted in 220/350 cases and were associated with a h igher case fatality rate (82% vs. 21%, P < 0.0001). After the introduction of Hib immunization in children, invasive Hib infections in unimmunized adu lts also declined, but the overall rate of invasive Hi disease in adults in creased, with most infections now caused by non-capsulated strains. Physici ans and microbiologists should be aware of the changing epidemiology, the h igh associated mortality and high risk of underlying disease. Invasive haem ophilus infections in adults should be investigated and treated aggressivel y.