Four people have been hospitalised and 11 cases of E.coli have been confirmed following visits to a farm shop in South Ribble.
Public Health England said all cases had visited lamb feeding events at Huntley’s Country Store, Salmesbury.
Dr Ken Lamden, consultant in health protection for Public Health England, said: “Investigations are still on going and all public health measures have been put in place.
“The owners are co-operating fully and we are working closely with them and with colleagues across health and local authorities.
“Symptoms of E.coli O157 include bloody diarrhoea, which can be serious, or milder forms of the infection which are usually self-limiting and clear within seven days.
“It is believed the outbreak began before Easter. Anyone who visited the lambing event between March 29 and April 24 and who is unwell with diarrhoea, bloody diarrhoea or passing less urine than usual should seek medical advice or contact NHS 111.
“To date we are aware of 11 laboratory confirmed cases of E.coli O157. Four people have been hospitalised with complications arising from the infection - one of whom has now left hospital and is recovering at home.”
There is no longer any risk to the public at Huntley’s, as all contact between animals and the public at the premises has now ceased.