Effect of short-term exposure to air pollution and pollen on medical emergency calls: a case-crossover study in Spain

Background: A symmetric case-crossover design was used to analyse the short-term relationship between air pollution, pollen and emergency calls to medical services. Methods: This study covered patients who made medical emergency calls in the City of Vigo (Spain) during the period 1996-1999. Morbidity data were obtained from the records of the 061 Medical Emergency Control Center, in its capacity as the body officially coordinating all medical emergencies by telephone. Air pollution data were furnished by the Vigo Municipal Air Pollution Surveillance Grid. Pollen levels were provided by the staff of the Spanish Aerobiology Network in Vigo. Results: A rise of 10 mu g/m(3) in ambient particulate levels led to the risk of medical emergency calls requesting attention increasing by: (i) 1.97% [95% confidence interval (95% CI): 1.83-2.11%] for circulatory causes on the same day; (ii) 1.95% (95% CI: 1.76-2.14%) for respiratory causes at 2 days and (iii) 1.34% (95% CI: 1.23-1.45%) for combined circulatory and respiratory causes on the same day. A number of pollens displayed a statistically significant relationship with emergency calls. No interaction was in evidence between pollens and air pollutants. Conclusions: While elevations in particulate air pollution increase medical emergency calls because of cardiac or respiratory causes or both combined, elevations in pollen levels increase medical emergency calls because of respiratory causes.