I've never heard of bacterial turning viral unless you get a secondary infection as those are 2 different bugs. Can always call your vet and ask. I know I called mine a ton when Harley, my beardie had RI as im pretty OCD about cleanliness and couldn't figure out how she got enterbacter. That's when she told about how that bacteria is just a common bacteria that is on everything pretty much and is mostly transferred through fecal to oral so could have gotten it from a food item that wasn't washed really well or possibly from a feeder bug that somehow came into contact with a reptile with it.
As for keeping humidity in, I personally cut a thick piece of cardboard to fit on the top of my tank. Then I cut a circle 1 inch or so bigger than the dome I use for the CHE in the cardboard where I wanted it, in this case the middle. Then I wrapped it the bottom with tinfoil and folded it over to the top and taped it in place. I then placed it over the top above the screen and put the dome light down on it. This keeps the heat in and humidity too. Also can put a large water dish half under the heat lamp/CHE and that will help a lot too. Doing both that, my BP cage can get as high as 75% humidity and that's in a 36x18x12 glass tank using aspen. You can also shift the light let or right depending if you need to raise the cool side or hot side more.
I wouldn't let the hot side get over 95f but the cool side could go up to 84f. I personally keep mine 83f on the cool side, 84-86f on the hot side depending on the day and 90f on the UTH on the hot side. My pied girl seems to love that setting as she pretty much lives in her hot side rock cave and pushes all the aspen from the floor of it into the doorway of the cave like closing a door. Then when she smells a rat, she busts the aspen door down and stands up like a cobra as I open the top
Oh also did the vet tell you what bacteria it was? Also you should see signs of improvement in a few days. The vet told me if you don't see signs of improvement in a few days, you might need to change antibiotics. This was for a bearded dragon but I imagine it would be the same for snakes and probably even more so in snakes as they really have only 1 functioning lung vs a lizard. But Baytril should work as its a broad spectrum antibiotic. Fortaz also works well I've been told