Number and risk of first aid visits and serious incidents associated with using different combinations of substances.

For each combination of substances, the risk of visiting a first aid station was calculated by dividing the number of first aid visits (FAVs) rrelated to that combination by the number of FAVs for that cohort.CI = 95% confidence interval. Confidence interval for relative risk (RR) of a serious incident (SI) was calculated using Morris and Gardner's [46] formula.The category no substance use is the reference category for the SI risk ratios.