Health bosses revealed today an E-coli outbreak has been detected in Kent.
Officials from the Health Protection Agency said the bug has spread in a family believed to be from Maidstone.
It is then thought to have been carried to Sussex.
One case has been confirmed and two others are being investigated.
The HPA said the common link was that all three cases are members of the same family who have mixed socially on several occasions in recent weeks, including family barbecues and picnics in the countryside.
The response is being led by Kent Health Protection Unit because the first case lives in Kent.
Unit Director, Dr Mathi Chandrakumar, said: "We are raising awareness of E.coli O157 infection especially as at this time of year people attend more barbecues and picnics in the countryside.
"It is an infection that can be passed easily from person to person and young children are especially vulnerable to it and to complications which can arise from it.
"We want to stress the importance of good hand hygiene in families where there is any diarrhoea illness.
"Adults should ensure they supervise children's handwashing - especially before eating and when visiting parkland or countryside picnic areas where there is a possibility that areas may have been contaminated with animal faeces."
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