CDC has developed two step method for testing Individuals with cases for the virus that causes Coronavirus Disease (COVID-19) and it works as follows - 

...CDC has developed a form that provides a standardized approach to reporting persons under investigations (PUI), as presumptive positive cases (individuals with at least one respiratory specimen that tested positive for the virus that causes COVID-19 at a state or local laboratory) and laboratory-confirmed COVID-19 cases (individuals with at least one respiratory specimen that tested positive for the virus that causes COVID-19 at a CDC laboratory)... cdc.gov

 Hope that helps explain the difference. 

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