Background: Changes in the incidence of coronavirus disease (COVID-19) over time in the US have coincided with shifts in clinical care for hospitalized patients and care-seeking behaviors of patients. These shifts are likely to influence the baseline characteristics of hospitalized patients over time.

Objectives: Describe trends in COVID-19 severity for inpatient COVID-19 patients at hospital admission, overall and stratified by race, ethnicity, and geographic region over the first six months of the pandemic, from March until August 2020.

Methods: Using de-identified Optum COVID-19 EHR data (March - August 2020), we defined a cohort of patients hospitalized with COVID-19 diagnosis or positive SARS-CoV-2 laboratory result. Among this cohort, we measured COVID-19 severity at admission using 3 mutually exclusive levels: No O2 (neither supplemental oxygen nor non-invasive ventilation [O2/NIV]) or intubation or invasive mechanical ventilation [IMV]), O2/NIV, or IMV. We plotted the distribution of COVID-19 severity at admission by month of inpatient admission overall, and stratified by US census region, race, and ethnicity. Trends for heterogeneity in the distribution of COVID-19 severity over time were evaluated using Cochran-Armitage trend test overall and by region, race, and ethnicity, and plots of percentages over time were visually inspected to identify direction of the trend.

Results: The percent of admissions with the highest COVID-19 severity recorded (IMV group) decreased from March to August (from 12.6% to 3.9%, p for trend <0.01), as did admissions among the O2/NIV group (51.4% to 42.3%, p <0.01). These trends were similar when stratified by region, except in the Southern US region where the O2/NIV group increased over time (38.3% to 43.1%, p<0.01). The most dramatic change was a decrease from March to August in admissions in the IMV and O2/NIV subgroups in Northeast US (13.3% to 0.3% and 48.8% to 17.9%, respectively). Similar trends were found from March to August for IMV and O2/NIV when stratified by race (Black or African American: 11.4% to 2.9% and 52.1% to 40.1%, respectively; White: 12.9% to 4.1% and 54.3% to 40.1%; Asian: 19.4% to 0% and 47.8% to 31.2%) or ethnicity (Hispanic or Latino: 14.0% to 4.3% and 47.7% to 36.1%).

Conclusions: The percent of patients requiring IMV and O2/NIV at admission decreased over calendar time from March through August 2020. Changes in severity at admission over time may be driven by several factors, including increased understanding of the COVID-19 disease process, availability of treatments, and evolving perspective on ventilation.