Health officials are investigating possible cases of a bug which has been linked to a Lincolnshire farm open to the public.
A spokesman for Public Health England said it is investigating possible cases of cryptosporidium associated with Bowthorpe Park Farm, near Bourne.
The parasite causes severe stomach upsets in children and adults with low immune systems.
Environmental health officers from South Kesteven District Council have also been involved in the investigation, with 13 cases confirmed by its officers.
The council said the farm had precautions in place and there was no ongoing risk to the public.
A spokesman for Bowthorpe Park Farm said the investigation was closed and no link had been established with their premises. The spokesman said the farm had all the right precautions in place to safeguard visitors.