 Such studies distinguish between exposures that are risk factors for both COVID-19 and other respiratory infections, and exposures that are risk factors for just COVID-19 or just for other respiratory infections. Incorporating the test-negative design into on-going testing efforts is useful in itself, but it would be more useful with the addition of the matched case-control designs .
<coherence>  Such studies distinguish between exposures that are risk factors for both COVID-19 and other respiratory infections, and exposures that are risk factors for just COVID-19 or just for other respiratory infections. Incorporating the test-negative design into on-going testing efforts is useful in itself, but it would be more useful with the addition of the matched case-control designs .
 Such studies distinguish between exposures that are risk factors for both COVID-19 and other respiratory infections, and exposures that are risk factors for just COVID-19 .