Health officials are investigating an outbreak of E. coli O157 which may be linked to a petting farm in Brecon.
Two children from Ceredigion and Kent who visited Cantref Adventure Farm have been affected by the bug and are recovering at home.
Two family members of one of the infected children have also tested positive.
A farm spokesperson said direct contact between animals and the public at the farm had been stopped as a precaution.
One of the infected family members is believed to have contracted the illness through contact with the child.
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