An investigation is under way into an E coli outbreak that affected two children and others is being linked to animals at a petting farm in Mid Wales.
Health officials said the type of infection - E coli 0157 - confirmed in two children exactly matches samples at a Brecon petting farm.
Public Health Wales and colleagues in three local authorities and the Health Protection Agency have been investigating the outbreak since September.
Both children had visited Cantref Adventure Farm in the days before they became unwell, and both are recovering at home.
Three other people, who are family members of the infected children, have also tested positive for the same type of E coli 0157.
One is believed to have contracted the illness at the same time, but does not have symptoms. The other two became ill at a later date and are believed to have contracted the illness through contact with the child.
Powys County Council's environmental health department is working with Public Health Wales to investigate the outbreak, along with the Environmental Health departments in Ceredigion and Kent where the children are resident.
The farm was advised to continue to stop direct contact between animals and members of the public while the exact source of infection is investigated.
The outbreak control team is now working with the farm owners to identify any further measures that need to be put in place.
E coli 0157 is a serious infection that causes severe diarrhoea, sometimes with blood in it, abdominal cramps and fever. In children, it can cause kidney failure that can prove fatal.
Mac Walapu, consultant in communicable disease control for Public Health Wales, said: "It is difficult to say whether we will see further cases of E coli 0157 linked to the farm, but if anyone who has visited the farm since the beginning of August has symptoms, they should still contact their GP as soon as possible.
"The infection can pass from person to person and so it is important that anyone who is ill should observe strict personal hygiene to avoid spreading the infection.
"We are therefore urging everyone to wash and dry their hands thoroughly after going to the toilet, after handling animals and before preparing or eating food. Parents should supervise young children while washing their hands. Disinfecting all areas of the bathroom regularly, including hard surfaces and toilet and door handles, can also help limit the risk of further infection.
"Anyone who is unwell with E coli 0157 should stay away from school, nursery or work while they have symptoms and until they are advised that they are well enough to return."
Health officials said it was not uncommon for outbreaks of E. coli 0157 to be associated with children having contact with farm animals.
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