Here's just a couple basic recommendations to avoid this problem:
- Clean your toilets regularly, but if you are using harsh chemicals, after they've dried, wipe down with water or at least a wet cloth to remove any left over caustic ingredients. You'll have to let the toilet dry first in order for the chemical cleaners to maximally disinfect.
- Stick with the good old plastic toilets which can be cleaned easier and are less allergenic than wooden toilet seats. However, you can always cover the seat as well.
- And a personal caveat . . . avoid using public restrooms if possible :-)