How do doctors who treat for mild covid know that they are actually treating mild covid?

What is “mild covid?” Mild covid symptoms are essentially the same as the flu’s symptoms. So there is a vagueness problem here. Both mild covid and flu are “Influenza-Like Illnesses” (ILIs).

But maybe the new Multiplex Assay Test, which is based on PCR, can help. PCR detects RNA fragments and cannot distinguish between RNA fragments and live virus. So PCR can only show exposure; it cannot determine the cause of the clinical disease. The patient arrives at the clinic showing symptoms of an ILI, then gets tested for covid and various types of influenza. Each test has a false negative rate and a false positive rate. And even true positives can still mean that there is no live virus present.

How can PCR tests return a true positive when there is no…