A two-year-old girl has died and another two children are ill after contracting E.coli O157.
The child, from Ballantrae, South Ayrshire, died on Saturday after being taken to Glasgow's Royal Hospital for Sick Children.
Two other children from the Dumfries and Galloway area, whose family had contact with the little girl from Ayrshire, have also tested positive for the E.coli bug.
The youngsters, aged one and three, were admitted to Dumfries and Galloway Royal Infirmary at the weekend but have since been discharged.
Dr Carol Davidson, director of public health at NHS Ayrshire and Arran, said: "Investigations into the source of the infection are ongoing, but at the moment we have no reason to believe that others outside the families affected and their contacts are at any increased risk."