"C. S." wrote in message
My cat was exonerated. However, the old wallpaper around one of the
toilets had evidence of a human marking their territory (or missing
the target) on many occasions.

Do I have to replace the wallpaper (it superficially looks fine, so I
would rather not bother), or is there a way of sanitizing/cleaning the
wallpaper? The thought of invisible bacteria hiding in the wallpaper
grosses me out and worries me since I have my first child on the way
in January.

It happens in every household. Invisible droplets or water splash during
urination and flushing. It can land as far as 6 feet away.

OTOH, urine is actually not harmful. Your first (and every) child will be
bathed in it in their diapers, just like the rest of us have for centuries.

I'd replace the paper with something washable, but don't panic about
bacteria. If anything, I'd fear using anti-bacteria soap as it kills the
good with the bad and breaks down the body's ability to deal with it.
Ed