I have decided to put a link here about E Coli and some other bacterial diseasesYour best bet would be to have routine fecals done and to deworm at least twice a year, but that's no guarantee. I watch mine like a hawk and if one starts to look iffy I examine examine it's poop. If the poop is even slightly yellow I worm with Safeguard at 50mg/kg (.5ml per 2.2 pounds) and start metronidazole at ~60mg/kg once a day for five days. Depending on what the poop looks like, I might also start Baytril.
As for preventing it, you could try the Histostat-50, but I think that's meant to be fed daily and it is toxic to ducks, geese and dogs. Some people say you can use acidified copper sulfate as a preventative, but I don't know anything about it.
-Kathy
http://msucares.com/poultry/diseases/diseases.html