If you are sure it has been cleaned AND disinfected over the entire inside AND outside as well as the seat, as well as the surrounding floor area, then you might have a leaking wax seal, which sits under the toilet and seals between the toilet and the drain. I would doubt this is the case, because the urikne get pretty diluted in flushing, so would not likely leave a urine smell if leaking out under the toilet base.
Replacing the wax seal requires disconnecting and pulling the toilet off, fixing any drain flange problem, putting on a new wax seal, and reseating the toilet. It is something you can do yourself if you are a handyman, but if you are not pretty confident in your abilities maybe pay a plumber $100-150 or so to do it.
Be prepared, however, for the possiblity that if it has been leaking for long, then the subfloor and joists might have rot, involving a MUCH more significant repair job.
I presume here you are a homeowner - if you are a renter, this type of repair would usually be the landlords responsibility.