In general, bacteria and viruses do not survive long outside the body (the organisms die in minutes to hours), hence they do not spread via toilet seats, swimming pools etc. However, they may be transmitted via bodily fluids such as semen and vaginal fluids, especially so if there is a break in the skin or mucosal membranes. Please see a doctor if you suspect that you may have contracted an STD as thorough follow-up and investigations are required.