Influence of pollen level on hospitalizations for asthma.

The effect of pollen level on asthma hospitalizations is still under debate. The aim of this study was to analyze hospital admissions due to asthma and its relation with environmental pollen and meteorological factors. During 13 years, we included every patient admitted with asthma as primary or secondary diagnosis. For this purpose, we used a case-crossover analysis to compare pollen concentrations at the time of admission with values of the same variables 2 to 6 days before admission. We included 6,687 hospital admissions. High maximum temperature and low humidity were associated with lower risk of asthma admissions. High mean pollen levels exerted a moderate effect and high maximum pollen levels led to a dramatic increase of hospital admissions due to asthma, especially among females. In conclusion, environmental pollen level increases the risk of asthma hospital admissions.