Background: Hospitals experience winter surges in admissions due to respiratory infections. The roles of acute bronchitis and influenza-like illness (ILI) in the timing and severity of these surges are examined over the years 1990-91 to 2004-05.
Methods: Respiratory admissions of persons aged > or =65 years in England and Wales were analysed in relation to patients with ILI or acute bronchitis diagnosed by community-based general practitioners from a sentinel surveillance network.
Results: Acute bronchitis and ILI accounted for 46 and 7% of the variation in respiratory admissions, respectively: when admissions were lagged by 1 week, these estimates were 20 and 14%, respectively. Admissions peaked in weeks 52, 01 or 02 (late December to early January) in 14 of the 15 winters. Acute bronchitis peaked during weeks 01 or 02; ILI exhibited greater variability and peaks ranged from weeks 46 (mid-November) to 07 (mid-February). During winters where acute bronchitis and ILI peaked concurrently, surges on hospitals were most severe.
Conclusions: During each winter acute bronchitis provides a consistent and major contribution to the winter admissions surge in the elderly. The variable incidence of ILI can increase the surge in admissions, especially when ILI and acute bronchitis peak together.