I've never heard of such a thing. When a turt has RI, the vet will administer a series of antibiotic injections to treat it. Think of the last time you had tonsilitis or something similar. The doc gave you antibiotics to treat it. We don't take them to prevent it tho.
The best thing you can do to prevent ANY illness or injury for your turt is to keep the right temps and keep them constant, vary the diet and make sure the tank is large enough for swimming so he gets exercise. keep the tank away from any windows or air conditioning vents and make it escape-proof and keep any other pets (cats for example) away from the tank.
One more thing...don't worry so much
We were all new at this at some point and I know I was paranoid about illness and such but as long as you know you're giving him the best care you possibly can, you'll both be fine!
The things that come to those who wait may be the things that were left by those who got there first - Steven Tyler