S1 Dataset -

Objective
Pandemic-associated stress may have exacerbated preexisting mental health and substance use disorders (MH/SUD) and caused new MH/SUD diagnoses which would be expected to lead to an increase in visits to emergency departments and hospital admissions for these conditions. This study assessed whether the proportion of hospital and emergency department encounters for MH/SUD diagnoses increased during the first year of the COVID-19 pandemic in the United States.
Methods
We conducted a longitudinal (interrupted time series) analysis of 994,724 eligible encounters identified by electronic query between January 1, 2016 and March 31, 2021. Of these, 55,574 encounters involved MH/SUD diagnosis. The pre-pandemic period was defined as January 1, 2016 to March 31, 2020, and the pandemic period was defined as April 1, 2020 to March 31, 2021. All statistical analyses were performed with R.
Results
No significant trend in MH/SUD encounters at baseline (rate ratio 1.00, 95% CI 0.99–1.01, p = 0.75) was observed. However, the onset of the pandemic was temporally associated with a significant level increase in the proportion of MH/SUD encounters relative to overall encounters (rate ratio 1.14, 95% CI 1.06–1.21, p<0.001) with no change in the overall trend (rate ratio 0.99, 95% CI 0.90–1.10, p = 0.89).
Conclusions
The significant pandemic-associated increase in the proportion of MH/SUD encounters relative to overall encounters was driven largely by sustained numbers of MH/ SUD encounters despite a decrease in total encounters. Increased support for mental health care is needed for these vulnerable patients during pandemics.