A time-series approach for estimating emergency department visits attributable to seasonal influenza: results from 6 US cities, 2005-2006 to 2016-2017 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 6 US cities during influenza seasons from 2005-2006 to 2016-2017. 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 visits. 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 6 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 vs 58 per 100 000 population (95% CI, 45-71) for hospitalization. This difference was particularly large for the 0-4 years age group: 911 per 100 000 population (95% CI, 558-1263) for total ED visits vs 43 per 100 000 population (95% CI, 15-71) for hospitalization. This study highlights the substantial burden of influenza on emergency health care services and the importance of integrating such data into public health planning and influenza management strategies.