Families have been urged to follow “safety precautions” as new cases of E.coli have emerged amid a continuing outbreak.
NHS Lothian, along with local and national partner agencies, have said that the total number of confirmed cases now sits at 48.
It comes after sickness symptoms at Musselburgh Private Nursery, which was closed as a precaution, were confirmed as E. coli on Friday.
All staff and pupils affected have now been formally excluded under the Public Health Act and informed of the actions they need to take.
The infection has also been identified in cases linked to Church Street Pear Tree Nursery and Meadowpark Pear Tree Nursery, both in Haddington.
West Road Pear Tree Nursery remains closed as a “precaution”, but no cases of E. coli have been confirmed.
So far, medics have been unable to identify a specific source, but advanced microbiological testing is ongoing to determine the strain of the infection and any links.
Investigating the outbreak, Dr Graham Mackenzie, consultant in Public Health Medicine and Chair of the Incident Management Team (IMT), said it was “vital” that parents and carers follow the instruction to self isolate.
He said: “It is crucially important that families understand that this is a rapidly evolving situation and it is affecting the lives of hundreds of people. We need everyone to work with us to bring an end to this outbreak as swiftly as possible.
“If you have been given an exclusion order, it means that you must self-isolate at home, just as we have all done with Covid-19. You must not go to work or school, the shops, the playpark or to parties and sleepovers.
“As soon as two negative samples have been returned, families will be allowed to return to normal.
“We have already lifted scores of exclusion orders for pupils, parents and staff. There is light at the end of the tunnel and as soon as enough exclusions are lifted and investigations are complete, nurseries will be able to reopen.
“However if families choose to mix with others when they have been instructed to self-isolate, they are putting themselves and others at risk.
“They may unknowingly come into contact with someone who has the infection, but not yet been confirmed. That would not only mean that they could develop the infection, but that they would start the exclusion period all over again because they have come into contact with a confirmed case.”