
Flu A
According to the CDC, molecular assays, including RT-PCR, are recommended for testing respiratory tract specimens from hospitalized patients because of their high sensitivity and high specificity.

Flu B
The Infectious Diseases Society of America (IDSA) recommends use of rapid influenza molecular assays over rapid influenza diagnostic tests (RIDTs) for detection of influenza viruses in respiratory specimens of outpatients.

COVID-19
The current gold standard is to perform reverse-transcription polymerase chain reaction (PCR) on nasopharyngeal samples. Best-in-class assays demonstrate a limit of detection (LoD) of approximately 100 copies of viral RNA per milliliter of transport media.