The full sentence he's reading is, The 2019 novel coronavirus RNA is genetically detectable in upper and lower respiratory specimens during infection. Positive results are indicative of active infection with 2019 novel coronavirus, but do not rule out bacterial infection or co-infection with other viruses. The agent detected may not be the definite cause of disease. You can easily see the trick Alex is playing here. He starts the sentence at, quote, do not rule out, which changes the grammar of the sentence. When you start the sentence that way, it appears to be a command, telling people to do something. When in reality, the sentence starts with, quote, positive results are indicative of active infection, but do not rule out. Which is saying that a positive result would show COVID-19, but also that doesn't mean the patient may not be suffering from another condition also.