Counting Coronavirus Disease-2019 (COVID-19) Cases: Case Definitions, Screened Populations and Testing Techniques Matter

While counting cases of disease appears straightforward, there are issues to consider when enumerating disease counts during an epidemic. For example, for Coronavirus Disease-2019 (COVID-19), how is a case defined? Hubei province in China changed its case definition twice in a fortnight—from laboratory-confirmed cases to clinically confirmed cases without laboratory tests, and back to laboratory-confirmed cases. This caused confusion in the...