You shouldn't be at a loss. I don't think any kind of virus or what we know of as viruses can be stopped by cleaning. I don't think it's fully understood, not by us, or by "professionals". I wouldn't rack my brain over it, especially since it appears you're doing all you can do. Our immune system is a funny thing, not fully understood either. I'm certainly no doctor, but I can tell you I know our immune systems don't like overexposure to chemicals either. Like my eczema reaction. That's the immune system working overdrive for what it senses as trouble.Here's what we use. There's other stuff but good old E04 makes up the mainstay. I use it to wipe off toilets. When I swish the bowls with a brush I use a 5/1 bleach mix, let it set overnight in the bowl. Same with urinals & the "frisbees" are replaced monthly.
I also leave the toilet bowl ring/seats up when I finish. This signals to me I've disinfected, cleaned a toilet, move to the next. It also lets the disinfectant air dry over night to kill whatever is there.
I also wipe down the sinks in restrooms, soap containers, paper towel dispensers. The floor gets sanitized and "bright" mopped with my own mix of E04 and I think its E09. I cannot smell that my bathrooms are clean, no sense of smell, but I do know when I've cleaned one, it's clean.
Others have said I do damn well at cleaning bathrooms. They fear going in to check behind me because I make them worry about their job security. I dare people to check my stuff, they know better.
That's why I'm kind of at a loss. I've instilled that mentality in most of the crew. Then too, it might instill someone with hate enough to bring something in to spread deliberate. Not saying outright that's the case but certainly there's room to speculate.