Respiratory effects of sulphur dioxide: a hierarchical multicity analysis in the APHEA 2 study

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Abstract
Background: Sulphur dioxide (SO2) was associated with hospital admissions for asthma in children in the original APHEA study, but not with other respiratory admissions. Aims: To assess the association between daily levels of SO2 and daily levels of respiratory admissions in a larger and more recent study. Methods: Time series of daily counts of hospital emergency admissions were constructed for asthma at ages 0–14 years and 15–64 years, COPD and asthma, and all respiratory admissions at ages 65+ years in the cities of Birmingham, London, Milan, Paris, Rome, Stockholm, and in the Netherlands for periods of varying duration between the years 1988 and 1997. A two stage hierarchical modelling approach was used. In the first stage generalised additive Poisson regression models were fitted in each city controlling for weather and season. These results were then combined across cities in a second stage ecological regression that looked at potential effect modifiers. Results: For an increase of 10 μg/m3 of SO2 the daily number of admissions for asthma in children increased 1.3% (95% CI 0.4% to 2.2%). Effect modification among cities by levels of other air pollutants or temperature was not found. The SO2 effect disappeared after controlling for PM10 or CO, but correlation among these pollutants was very high. Other respiratory admissions were not associated with SO2. Conclusion: SO2 is associated with asthma admissions in children, indicating that reduction in current air pollution levels could lead to a decrease in the number of asthma admissions in children in Europe.