The chain has introduced its own E.coli policy and said it will close any nurseries where a case is suspected to stop it spreading.
On Monday, NHS Fife confirmed the number of cases linked to the nursery as 13.
It is understood that Careshare was informed of the first E.coli case on 5 May. Information from NHS Fife received by the nursery stated, 'It is not thought that the infection came from the nursery or that anyone else at the nursery is likely to be at risk.'
Officials did not advise the nursery to close until 9 May after a second case was confirmed.
Careshare operations director Jonathan Bell said, 'From now on Careshare will not wait for official advice if there is any E.coli case connected to a nursery. A single case suspected by a doctor will result in immediate closure of the nursery to prevent further spread.'
Meanwhile, the Care Commission confirmed that it would carry out unannounced spot checks at Careshare's nurseries and a detailed review of their infection control procedures.