This is not the Dr's form, but you can not get an STD from a toilet seat.
I guess I would have to do some further research myself. Vance2335, from what I've seen, is a very knowledgeable person; however, I WAS under the impression that you could get crabs from a toilet seat. Crabs (pubic lice) are actual organisms that bite. If one individual has them and you have close contact with that person (not necessarily intercourse), you can get crabs.
Thank you anxiery1569. I was referring to STD's like HIV, gonorrhea and others. Crabs I can not say for sure if you can get those or not from a toilet seat, but you can not get anything like gonorrhea, syphillis, herpes, HIV and others.