[Stenosing laryngotracheitis (pseudocroup) and sulfur dioxide content of the air. Results of an 18-year retrospective long-term study of possible spatial and temporal relations].

Based on the immission levels measured in the city of Bochum (approx. 20,000 readings), 1200 hospitalized children with pseudocroup were examined for a possible relationship between croup incidence and sulphur dioxide levels. Evaluation according to geographic location showed no statistically significant correlation between croup incidence and SO2 levels over a test period of 13 years. Only for 3 of 13 years did Spearman's rank correlation coefficient show a weakly significant positive correlation (P less than 0.05). In one test year, however, there was a statistically significant negative correlation (P less than 0.025). Evaluation of the 16-year study in terms of time-dependent relationships yielded no significant deviation of pseudocroup incidence from the expected mean value for the individual SO2 concentration ranges. Over the period of this study, there was therefore no cause-effect relationship between sulphur dioxide levels and pseudocroup incidence.