Abstract
OBJECTIVES: During the 2009 influenza A (H1N1) pandemic, unusual influenza activity outside the typical winter season provided a unique opportunity to evaluate the association between influenza and pneumonia incidence. We sought to quantify the impact of the 2009 pandemic on the incidence of emergency department (ED) visits for pneumonia in the United States (US). METHODS: Using the Nationwide Emergency Department Survey, we estimated monthly counts and rates of excess all-cause pneumonia ED visits in the US attributable to the pandemic by comparing observed pneumonia ED visits during the pandemic (April 2009-March 2010) to expected values modeled from the three prior years. RESULTS: The pandemic was associated with an excess of 180,560 pneumonia ED visits or 0.59 excess pneumonia visits per 1000 US population (95% confidence interval: 0.55, 0.62). These excess visits accounted for 7.0% of all pneumonia ED visits during the pandemic year. The greatest excess occurred during months with highest influenza activity (September-November 2009). Persons aged <65 years accounted for 94% of the excess pneumonia visits. CONCLUSIONS: ED visits for pneumonia increased substantially during the 2009 pandemic, especially during peak influenza activity, suggesting a strong association between influenza activity and pneumonia incidence during the pandemic period.