Air Pollution Increases Influenza Hospitalizations

Gregor Singer; Joshua Graff Zivin; Matthew Neidell; Nicholas Sanders

Our analysis utilizes patient level data on inpatient hospitalization (39), which allows us to focus on severe cases specifically limited to influenza (for details on data, descriptives, and empirical methods see Supplementary Appendix S.1, S.2 and S.3). Our principal outcome of interest is the number of inpatient ad-missions per county-month where the primary diagnosis is influenza according to the International Classification of Diseases (ICD) (40). We combine this with high frequency air pollution readings of local ground monitors across the U.S., as well as data on local temperature, specific humidity, precipitation and wind speed (41). The richness of our data allows us to control for a wide variety of both regional and temporal controls. Our preferred specification includes county-by-year and month-byyear fixed effects. County-by-year effects control for differences in unobserved characteristics such as demographics, socio-economic factors, and health care access and protocols that influence pollution exposure and health outcomes across counties separately for each year. The month-by-year fixed effects control for general monthly and seasonal trends within each year in both influenza and pollution (42).