Last month's outbreak of E.coli O157 at Rose Lodge Nursery in Aboyne, Aberdeenshire saw 3 babies requiring hospital treatment and another 4 confirmed cases. One child is still in hospital.

A subsequent investigation by the NHS Grampian Health Protection Team and Aberdeenshire Council Environmental Health Department has found that the infection was most likely introduced into the nursery by a child and spread by "staff having failed to maintain an adequate standard of hand hygiene".

A spokesman for the NHS said: "The investigation indicates this child did not have any diarrhoeal symptoms while in the nursery, but may have been excreting E.coli O157 bacteria in its faeces for a number of days, before developing symptoms. The child became obviously unwell at home and did not attend the nursery again until fully recovered.

"The investigation has shown that the E.coli O157 bacteria infecting this child was transmitted to three children and two adults attending the baby room within the nursery. The investigation team has concluded that the most probable transmission route for the infection was through nursery staff having failed to maintain an adequate standard of hand hygiene in the baby room."

Nursery management cooperated fully with the investigation and have made improvements in response to NHS advice. There have been no new cases in those attending the nursery after control measures were put in place by the investigating team.

A full report of the investigation should be compiled over the next few weeks.