The bug can cause discomfort

An outbreak control team from NHS Grampian, the area's health board, met on Friday to discuss a strategy aimed at tackling the outbreak in the Aberdeen area.

The infection is uncomfortable for most healthy adults but they rarely need to be admitted to hospital for treatment.

However, it can cause severe illness in people with immune problems.

The bug has an incubation period of about seven days.

North of Scotland Water Authority (Noswa) said that it was examining ways of improving the treatment process at the Invercannie water works.

A spokeswoman for NHS Grampian said: "Water is regarded as a possible source.

'Precautionary measure'

"The cause of the outbreak is not conclusively known. Noswa is continuing its investigations.

"In addition, Noswa is exploring the feasibility of further boosting the treatment process at Invercannie as a precautionary measure.

"The advice to the public remains that, on the basis of currently available evidence, there is no need for the public to take any special precautions."

A Noswa spokesman said: "The health board is saying that people can still drink the water.

"The cause of the outbreak is not known - water is one of the ways that the organism is able to spread."

He said Noswa was investigating the possibility of using a process in which water could be further cleansed at treatment plants.