Table 3.

Expected variation in positive predictive value (i.e. probability that a case meeting the diagnostic criteria is truly ill with COVID-19) by COVID-19 incidence

COVID-19 incidence	Background incidence of diseases with overlapping signs and symptoms (consider the patient’s age and comorbidities, the geographic setting and season)	Modality of COVID-19 diagnosis
		Testing	Syndromic
High (around the peak)	Low	Very high	High
	High	Very high	Low to moderate (for mild and moderate cases) Moderate to high (for severe cases)
Medium (just after or just before the peak)	Low	Very high	Moderate to high (for mild and moderate cases) High (for severe cases)
	High	High	Moderate (for mild and moderate cases) Moderate to high (for severe cases)
Low (early or late in the epidemic)	Low	High	Low to moderate (for mild and moderate cases) Moderate to high (for severe cases)
	High	Moderate to high (depends on test specificity)	Very low (for mild and moderate cases) Low (for severe cases)