The BBC's Pennie Taylor reports from Ayr

Ayrshire and Arran Health Board is sending out letters to the former patients on Monday, offering them blood tests and counselling.

It follows news that two former patients at Crosshouse hospital in Kilmarnock have contracted the liver virus, hepatitis B, which is potentially fatal.

The cases came to light in July and the two have since recovered.

However, it was not until mid-October that the source of the infection was identified and it has taken a month to set up a helpline to cope with the response.

Already about 200 people have called the helpline.

Traced

Health officials have now traced it to a female junior doctor who worked on Crosshouse's general surgical ward from 1 August 1997 to 31 January this year.

Two patients at Crosshouse hospital have contracted hepatitis B

The doctor, who now works overseas, also worked on Ayr hospital's general medical ward from 1 February this year to 31 July.

The health board says she did not know she had hepatitis B when she worked at the hospitals.

Hepatitis B affects can be carried for years with no visible symptoms and it is usually expelled from the body within 13 weeks of infection.

It is thought that around 50,000 people in the UK may carry the virus.

Some will only go on to show flu-like symptoms, but in rare cases the virus, if left untreated, can cause liver failure.

Hepatitis B is carried in body fluid and can be transmitted through sharing needles, blood transplants and sex.

Warning

Ayrshire and Arran Health Board have been working with local GPs to identify all the patients affected.

They have written a letter to them, telling them they have "a very small chance" of developing the disease.

Blood tests and counselling are being offered and a helpline has been set up to give advice about the virus.

The helpline number is 0800 224488.

Dr Drew Walker, the board's director of public health, said: "The level of risk is really very low. We won't be at all surprised if we don't find anybody [else infected]."