Rainfall-Associated Bronchospasm Epidemics: The Epidemiological Effects of Air Pollutants and Weather Variables

BACKGROUND This study compares different risk factors in patients visiting a hospital during five rainfall-associated bronchospasm epidemics in Ahvaz and those visiting on other occasions. METHODS This case-control study was conducted on 5307 patients with bronchospasm admitted to the Emergency Department of Imam Khomeini Hospital in Ahvaz (Iran) from late October to December (as the epidemic) and 916 patients admitted from late January to March (as the nonepidemic) in 2011 to 2015. RESULTS A total of the 41.7% of the cases and 48.8% of the controls had episodes of bronchospasm, suggesting a significant difference between the two groups (P < 0.001). The mean concentrations of PM10, NO, NO2, and NO x pollutants (except O3) were significantly higher in the nonepidemic periods (P < 0.05). The adjusted analysis showed a direct significant relationship between emergency respiratory admissions and each unit of increase in NO and SO2 concentration during the epidemic periods and NO2 concentration during the nonepidemic periods. During the epidemic periods, a direct and significant relationship was also observed between respiratory admissions and each unit of increase in relative humidity and evaporation. CONCLUSION The results suggest that certain pollutants and weather variables are associated with the risk of emergency respiratory admissions during epidemic periods.