Incidence and Determinants of COVID-19 in Patients Seeking Treatment for Substance Use Disorder: A Patient-Based Linkage Study.

People with substance use disorder (SUD) may be at increased risk of COVID-19 infection. However, there is little evidence regarding the incidence of and determinants associated with infection in this group. The aims of the study were to determine the cumulative incidence of COVID-19 among people who sought treatment for heroin, cocaine, cannabis, and alcohol use disorder in Catalonia; to identify sociodemographic, substance, and clinical determinants associated with COVID-19 infection among SUD patients; and to compare the cumulative incidence of COVID-19 infection in the population with SUD with that of the general population. A patient-based retrospective observational study was conducted. The study population comprised people who sought treatment for heroin, cocaine, cannabis, or alcohol use disorder in Catalonia in 2018 and 2019. We analysed cumulative incidence of COVID-19 (confirmed by PCR test) from 25 February to 31 December 2020. Additionally, we used a log-link binomial generalized linear model for COVID-19 infection, using the substance as the exposition, adjusting for sociodemographic and clinical variables. Of the 23,092 individuals who sought treatment for SUD, 38.15% were considered suspected cases of COVID-19, and 2.60% (95% CI = 2.41-2.82) were confirmed positive for COVID-19 by PCR test during the study period. Those who sought treatment for alcohol use (cumulative incidence of COVID-19 of 3% [95% CI = 2.70-3.34]) had a higher risk ratio than, those who sought treatment for heroin use (cumulative incidence of 1.94% [95% CI = 1.47-2.56]). Being born outside of Spain, living in an institutionalized residence, having HIV, and being in a high morbidity group were associated with higher risk of COVID-19 infection. Meanwhile, the cumulative incidence of COVID-19 in the general population, according to public COVID-19 test data, was 3.86% (95% CI = 3.85-3.87). This study did not find higher cumulative incidence of COVID-19 infection among people with SUD in Catalonia in 2020, despite the clinical vulnerability of this population and their social disadvantage. However, differences were seen in the cumulative incidence of COVID-19 according to the substance for which treatment was sought. For example, those with alcohol dependence had a higher rate than those dependent on heroin. Further studies are needed to determine the factors contributing to these differences.

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