Three tots confirmed to have the bug were yesterday treated in hospital, with one released.
Infection experts are trying to track down the source of the sickness and diarrhoea viral outbreak which hit the under-twos section at Rose Lodge Nursery in Aboyne, Aberdeenshire.
NHS Grampian said health protection teams found “reasonable” food hygiene and infection control at the unit.
A spokeswoman added: “Control measures are in place. An inspection has been carried out and an incident team convened.” The nursery, which has 40 pupils, first reported the virus on Sunday.
Experts say E.coli poses the biggest risk to under-fives.
Owner Julie Grant said: “We have taken the advice to close our Baby Room until further notice.
“The nursery remains open to unaffected families of children over two years old.
“We have a high standard of hygiene and rigorous infection control procedures. Our thoughts are with the children and families affected.”
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