Those in Portlaoise Hospital last month may have come into contact with the virus.
The HSE is advising people to be aware of the symptoms of measles, after a public health alert was issued in Laois on Friday.
It's warning people who attended the ED at Regional Hospital Portlaoise on Friday April, 26th, between 1pm and 6pm, they may have come into contact with the virus.
Anyone who was there between 2.40pm on Sunday and 6pm on Monday evening may also be affected.
Consultant in Public Health Medicine, Dr. Desmond Hickey, is warning people to be on the lookout for the following symptoms: