Using EHR data to identify coronavirus infections in hospitalized patients: Impact of case definitions on disease surveillance

•The number of cases identified with COVID-19 varies approximately twofold depending on whether laboratory confirmation is required in the EHR.•There is variability in laboratory testing over time, across region, and by patient demographics which may impact surveillance efforts.•Efforts to use the EHR to track novel diseases where testing may be limited and diagnostic codes are evolving should examine the impact of case definitions.