Influenza and adult hospital admissions for respiratory conditions in England 1989-2001.

Influenza is recognised as a major cause of excess hospital admissions during winter months. This study sets out to quantify admissions related to influenza during the last twelve winters and to examine the importance of age. Total admission data for respiratory disorders in adults for England during the years 1989 to 2001 have been used. Weekly admission data were examined in five-year age bands. Influenza epidemics were identified from clinical incidence data in the community. Baseline admission levels were determined by averaging weekly incidence data from weeks in which there was no clinical evidence of influenza activity. Excess admissions were estimated from the difference between observed and baseline admissions after adjusting the baseline in each group and year for the secular trend. Estimates for all adults were consolidated from the five-year age bands. Bed occupancy was estimated by applying data on average bed stay to excess admissions in age- and year-specific groups. We estimated 2.7% of all respiratory admissions were related to influenza. Excess admissions were strongly age related. Of the 16,227 annual average excess, 52% occurred in persons over 75 years. The excess admissions account for an average 145,544 bed days annually, two thirds (69%) in persons over 75 years. Annual excess bed occupancy was highest in 1999/2000 (39,512) though 30,000 excess admissions per year is not unusual. Hospital admissions due to influenza remain a major problem for health service delivery particularly in elderly populations. Though robust programmes of vaccination are needed, vaccination by itself will not eliminate the impact of influenza on hospital admissions in winter.