The association of wildfire smoke with respiratory and cardiovascular emergency department visits in Colorado in 2012: A case crossover study

Background: In 2012, Colorado experienced one of its worst wildfire seasons of the past decade. The goal of this study was to investigate the relationship of local PM_2.5 levels, modeled using the Weather Research and Forecasting Model with Chemistry, with emergency department visits and acute hospitalizations for respiratory and cardiovascular outcomes during the 2012 Colorado wildfires. Methods: Conditional logistic regression was used to assess the relationship between both continuous and categorical PM_2.5 and emergency department visits during the wildfire period, from June 5^th to July 6^th 2012. Results: For respiratory outcomes, we observed positive relationships between lag 0 PM_2.5 and asthma/wheeze (1 h max OR 1.01, 95 % CI (1.00, 1.01) per 10 μg/m³; 24 h mean OR 1.04 95 % CI (1.02, 1.06) per 5 μg/m³), and COPD (1 h max OR 1.01 95 % CI (1.00, 1.02) per 10 μg/m³; 24 h mean OR 1.05 95 % CI (1.02, 1.08) per 5 μg/m³). These associations were also positive for 2-day and 3-day moving average lag periods. When PM_2.5 was modeled as a categorical variable, bronchitis also showed elevated effect estimates over the referent groups for lag 0 24 h average concentration. Cardiovascular results were consistent with no association. Conclusions: We observed positive associations between PM_2.5 from wildfire and respiratory diseases, supporting evidence from previous research that wildfire PM_2.5 is an important source for adverse respiratory health outcomes.