Clinical significance
If RDT would be used in settings with a lower SARS-CoV-2 prevalence, such as 10%, a negative test would have a negative predictive value (NPV) of 98.6%. Such an NPV is acceptable if the patients do not belong to high-risk populations (severe cases, hospitalized patients). If the prevalence would be only 1%, the NPV would be 99.9%. Considering a specificity of 100%, other NPV, whenever for RDT or PCR, can be simply calculated using the following formula: (1-P)/1-SP (P = prevalence; S = sensitivity).Regarding the positive predictive value (PPV), even taking the lowest specificity confidence interval (99.3%), it would be 93% at 10% prevalence, which is high enough. At a lower prevalence, the PPV would drop, and the solution would be to restrict testing to patients with a high enough pre-test probability rather than confirming each positive case by PCR.