A Time-Series Approach for Estimating Emergency Department Visits Attributable to Seasonal Influenza: Results from Six U.S. Cities, 2005-06 to 2016-17 Seasons.

Emergency department (ED) visits during influenza seasons represent a critical yet less examined indicator of the acute burden of influenza. This study investigates the burden of influenza-associated ED visits in six U.S. cities during influenza seasons from 2005-06 to 2016-17. Using a time-series design, we estimated associations between daily ED visits and weekly influenza activity data from the Influenza Hospitalization Surveillance Network (FluSurv-NET). A counterfactual approach was then used to calculate attributable expected ED. Highest influenza-associated rates were observed among the youngest (0-4 years) and oldest (65+ years) age groups. Combining estimates across seasons, the influenza-associated ED visit rate for respiratory diseases was almost six times larger compared to the subset of ED visits that resulted in hospitalization: 364 per 100,000 population (95% CI: 294-435) for total ED visits versus 58 per 100,000 population (95% CI: 45-71) for hospitalization. This difference was particularly large for the 0-4 year age group: 911 per 100,000 population (95% CI: 558-1,263) for total ED visits versus 43 per 100,000 population (95% CI: 15-71) for hospitalization. This study highlights the substantial burden of influenza on emergency healthcare services and the importance of integrating such data into public health planning and influenza management strategies.