An investigation is underway into a cluster of cases of E. coli at a nursery that has seen children taken into hospital.
NHS Lothian, along with local and national partner agencies, is investigating 28 cases of the infection linked to Church Road Pear Tree Nursery in Haddington.
Another nursery has also been closed after a number of suspected cases developed there.
Although most cases have had mild symptoms and have not required hospital treatment, a small number of confirmed cases have been admitted to hospital, the health board said.
Some of these have been admitted as a precaution and all are in a stable condition.
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.
Those that have been affected have already been excluded and have submitted samples for testing, NHS Lothian said.
Cases, so far, have been confined to the nursery, respective households, or other close contacts. The nursery has been closed as a precautionary measure while the investigations continue.
A small number of people at a partner nursery in Haddington reported having symptoms of vomiting and diarrhoea – these have been resolved without needing medical treatment, the health board said.
As a precaution, Meadowpark Pear Tree Nursery in Haddington has been closed. All parents and carers have been notified.
Dr Richard Othieno, chair of the Incident Management Team and Public Health Consultant at NHS Lothian, said: “We know that this will be an anxious time for many of those who are directly affected by the infection. We have written to parents and carers of the children affected and to staff at the nursery to provide the most up to date information and ongoing health advice.
“NHS Lothian has a robust surveillance system in place to identify E. coli cases which helped us to identify these cases early and put in place essential control measures to prevent further spread.
“This outbreak reinforces the importance of washing hands regularly, particularly before eating or preparing food, and after going to the toilet.
“We continue to provide support to the nursery and those parents and carers who have been directly affected. We have encouraged parents to keep their children away from other children and those at higher risk until their negative results have been received”.
E. coli is a bacterial infection that causes illness in people. The symptoms range from mild loose stools to severe bloody diarrhoea. The most serious complications can lead to blood poisoning and kidney failure
There is no specific treatment for the infection and most people who are infected get better without medical treatment. However, those who have symptoms, or are concerned, are advised to contact their GP or NHS 24 on telephone number 111.
An outbreak closed a nursery in the Borders in May. Cherrytrees nursery in Hawick was forced to temporarily shut with anyone who attended or worked at the nursery, and who could have been exposed to the infection, told to stay at home and be tested to help contain the spread of the illness.
The outbreak in East Lothian comes after research revealed dangerous pathogens including norovirus and E.coli “colonise” plastic waste washing up on Scottish beaches long enough to cause harm to swimmers.
Researchers found imperishable items including cotton buds and wet wipes contained “concentrated reservoirs” of bacteria which could be picked up by humans after being pulled from popular bathing waters.