Supplementary Material for: Another Round: Influence of Alcohol-Related Conditions and other Drug Use-Related Disorders in Emergency Department Frequent Use. A single-site matched case-control study in Spain.

Introduction:
Patients who make 5 or more visits per year to hospital Emergency Departments (ED) are usually considered ED Frequent Users (FU). This study aims to better characterize the influence of alcohol and other drug use-related disorders in this phenomenon in a European Mediterranean country with public, universal, tax-financed healthcare system.
Methods:
Matched case-control study. Cases were adults between 18 and 65 years old who consulted 5 or more times the ED of a tertiary hospital in Spain between December 2018 and November 2019. Each case was assigned a control of the same age and gender, who appeared to the ED on the same day, but who made 4 visits or less to the service during the study period. The electronic record of the first ED visit during this period was used to extract the variables of interest: emergency care received, clinical and social characteristics. Predictors of frequent ED use were identified with conditional logistic regression.
Results: 609 case-control pairs (total n=1218) were selected. History of alcohol-related conditions (Adjusted Odds Ratio (AOR)=1.82 (95% CI 1.26-2.64) p= 0.001)and also other drug use-related disorders (AOR=1.50 (95% CI 1.11-2.03) p= 0.009) significantly increased the probability of frequent use of emergency services.
Discussion/Conclusion: Alcohol-related conditions and other drug use-related disorders must be evaluated in all ED FU. Specific action protocols to concurrently address repeated attendance and addictions in the emergency room could be a good tool to reduce frequent ED use.