AROUND 200 former hospital patients have been contacted because of concerns they may have been exposed to measles.
The letters were sent out by NHS officials after it was realised that two patients admitted to James Cook University Hospital had developed measles.
Test results last week confirmed the diagnosis.
As a precautionary measure, letters have been sent to around 200 people who were also inpatients on ward 3 and ward 15 to make them aware of possible symptoms.
However, officials think it is unlikely that any patients have been infected while they were in hospital, because the two patients who developed measles were cared for in single rooms.
Members of staff who were in direct contact with the patients have also been vetted by the trust's occupational health team.
Increasing numbers of measles cases are being reported across the UK.
It is highly infectious and is spread through direct contact with an infected person or through the air when an infected person coughs or sneezes.
Dr Richard Bellamy, from the trusts clinical infection directorate, said: "Although we are still waiting for official confirmation that the patients have measles, we have taken the precautionary measure of contacting patients who were on these wards at the same time.
"It's important to stress we do think the risk of anyone contracting measles is low but we wanted to minimise the chances of the illness being passed onto anyone else. The letters sent out basically explain the current situation, the symptoms to look out for and what people should do if these symptoms arise."
It usually takes about two weeks from catching measles to becoming ill. The early symptoms are a raised temperature, cough, runny nose, and red and watery eyes. The trademark rash of spots associated with measles normally appears a few days later on the neck or hairline and spreading down the body.
While there is no treatment for the illness, it can be prevented by the safe and highly effective MMR vaccine which is why parents are encouraged to check their child's vaccinations are up-to-date for their age.
Anyone who has concerns and has a fever and a rash should contact their local GP - or GP out-of-hours service - by telephone or NHS Direct on 0845 4647. They should not attend their GP surgery as measles is easily spread to others.