 This study aims to quantify the frequency of incidental hospitalizations over the first 15 months of the pandemic in multiple U.S. health care systems and apply electronic phenotyping techniques to improve COVID-19 hospitalization classification. The results show that a large proportion of SARS-CoV-2 PCR positive admissions were incidental, with straightforward EHR-based phenotypes differentiating admissions. This article was authored by Jeffrey G. Klan, Zachary H. Strasser, Megan R. Hutch, and others.