A probe at a fourth farm, closed in the wake of the E.coli outbreak, continued today after the Health Protection Agency (HPA) found a potential link with three sufferers.
World of Country Life farm, in Exmouth, Devon, was shut yesterday afternoon on the advice of East Devon District Council and the HPA.
The agency said it was "acting on information that potentially linked the farm with three individuals with confirmed E.coli O157 infection".
The farm has closed voluntarily and the local authority, HPA and its partners are conducting an investigation.
An HPA spokesman said: "There are many potential sources of E.coli and as yet there is no confirmation that the farm is the source of infection in these cases."
White Post Farm in Nottinghamshire was also shut after it was confirmed a second person was suffering from the same strain of E.coli as a previous visitor.
Godstone Farm in Surrey closed last Saturday and its sister farm, Horton Park Children's Farm in Epsom, is also shut because of "unsatisfactory" hygiene arrangements.
Hugh Pennington, emeritus professor of bacteriology at the University of Aberdeen, said "increased awareness" could be behind the rise in cases.
"Increased awareness by GPs, in particular sending in samples for testing, may be part of the reason why we're seeing an increased number of cases right now at the moment," he told BBC News 24.
According to the latest figures from the HPA there are 49 cases of E.coli linked to Godstone Farm in Surrey, including nine children. One of the youngsters was due to be allowed home today and the remaining children were in a stable condition, the HPA said.
An agency spokeswoman said it was not aware of any cases of E.coli O157 linked to Horton Park Children's Farm.
Tracy Mock, the mother of two-year-old twin boys Todd and Aaron Furnell, said she was "encouraged" by the progress they were making at St Thomas's Hospital in central London. They were admitted to hospital with kidney failure following the E.coli outbreak at Godstone Farm.
Anthony Moore, spokesman for White Post Farm, said its closure was "voluntary and precautionary".