People get sick, especially in autumn. And they infect each other. Reporting that some people working at the lab were sick, without any knowledge about kind of sickness is only going to add fuel to the conspiracy theories.
I suspect I had COVID-19 in the US late December 2019, but as of yet, the CDC doesn't acknowledge that possibility, and I've had enough exposure since that time that there's no reasonable way to test the hypothesis.
At a certain point, some of the investigations stop being practical to investigate further.