Air pollution and hospitalization for headache in Chile.

The authors performed a time-series analysis to test the association between air pollution and daily numbers of hospitalizations for headache in 7 Chilean urban centers during the period 2001-2005. Results were adjusted for day of the week and humidex. Three categories of headache-migraine, headache with cause specified, and headache not otherwise specified-were all associated with air pollution. Relative risks for migraine associated with interquartile-range increases in specific air pollutants were as follows: 1.11 (95% confidence interval (CI): 1.06, 1.17) for a 1.15-ppm increase in carbon monoxide; 1.11 (95% CI: 1.06, 1.17) for a 28.97-microg/m(3) increase in nitrogen dioxide; 1.10 (95% CI: 1.04, 1.17) for a 6.20-ppb increase in sulfur dioxide; 1.17 (95% CI: 1.08, 1.26) for a 69.51-ppb increase in ozone; 1.11 (95% CI: 1.00, 1.19) for a 21.51-microg/m(3) increase in particulate matter less than 2.5 mum in aerodynamic diameter (PM(2.5)); and 1.10 (95% CI: 1.04, 1.15) for a 37.79-microg/m(3) increase in particulate matter less than 10 mum in aerodynamic diameter (PM(10)). There was no significant effect modification by age, sex, or season. The authors conclude that air pollution appears to increase the risk of headache in Santiago Province. If the relation is causal, the morbidity associated with headache should be considered when estimating the burden of illness and costs associated with poor air quality.