Emergency department visits for migraine and headache: a multi-city study.

OBJECTIVES We set out to examine associations between ambient air pollution concentrations and emergency department (ED) visits for migraine/headache in a multi-city study. MATERIALS AND METHODS We designed a time-series study of 64 839 ED visits for migraine (ICD-9: 346) and of 68 495 ED visits for headache (ICD-9: 784) recorded at hospitals in five different cities in Canada. The data (days) were clustered according to the hierarchical structure (location, year, month, day of week). The generalised linear mixed models technique was applied to fit the logarithm of clustered daily counts of ED visits for migraine, and separately for headache, on the levels of air pollutants, after adjusting for meteorological conditions. The analysis was performed by sex (all, male, female) and for three different seasonal periods: whole (January-December), warm (April-September), and cold (October-March). RESULTS For female ED visits for migraine, positive associations were observed during the warm season for sulphur dioxide (SO2), and in the cold season for particulate matter (PM2.5) exposures lagged by 2-days. The percentage increase in daily visits was 4.0% (95% CI: 0.8-7.3) for SO2 mean level change of 4.6 ppb, and 4.6% (95% CI: 1.2,-8.1) for PM2.5 mean level change of 8.3 microg/m3. For male ED visits for headache, the largest association was obtained during the warm season for nitrogen dioxide (NO2), which was 13.5% (95% CI: 6.7-20.7) for same day exposure. CONCLUSIONS Our findings support the associations between air pollutants and the number of ED visits for headache.