As mentioned turtles are the main culprit with this illness. The reason the 4" rule came into effect is years ago fairs, carnivals and pet stores used to sell and give away thousands of wild caught sliders. They would be transported in horrible conditions and were a notorious breeding ground for disease. There were many cases of illness and people associated turtles with the disease not taking into account the horrid conditions these poor hatchlings were kept in. The truth is back then we didnt have the husbandry we have know. The 4" rule was in order to stop kids from putting their new baby turtles in their mouths and getting sick. In most cases animals with salmonella have been kept in filthy conditions, with turtles it just takes one to have it and since they share water, all turtles in tank are infected.