A third case of E.coli has been confirmed on a Scottish island.
NHS Orkney launched an investigation after two children who attended the same nursery in Kirkwall contracted the illness.
One of them, who was being treated in hospital, returned home on Tuesday. The other child, described as "a household contact" of the first one, is not showing symptoms.
NHS Orkney said last week that other children and staff from the nursery were being screened as a precaution.
During their investigations, health officials have identified a third confirmed case of E.coli O157 who has not been showing any symptoms.
The health board would not comment on whether the third case was also connected with the nursery. Officials are trying to find the source of the infection.
Dr Ken Black, consultant in public health medicine with NHS Orkney, said: "It is through our investigations that we have identified a third case and we are continuing to look for the possible source or sources of the infection.
"We continue to advise everyone to maintain vigilance concerning infection control.
"The spread of E.coli O157 infection can be prevented by following guidance on handling food and hand hygiene. As ever, anyone with health concerns should contact a health professional."
The E.coli O157 bacterium lives in the gut of animals such as cattle, sheep, deer and goats.
It can also be carried by pets and wild birds. In humans, the toxins that the O157 strain produces can cause diarrhoea and kidney failure as well as other illnesses.
Young children and older people are said to be at the greatest risk.
In August six cases of the strain were confirmed on the island.