People that were at the Waikato Hospital's Emergency Department late last month and early this month may have been exposed to the measles virus.
Three cases of the highly infectious disease have been reported in Waikato.
The Waikato Public Health Unit said the first case appeared to have been contracted overseas and on returning from thei trip, that person introduced the virus to the other two people.
Medical Officer of Health Felicity Dumble said during their infectious periods, all three people went to the Emergency Department (ED).
She said anyone who was at ED on Friday 25 March, Monday 4 April, or Saturday 9 April may be at risk of developing the disease, if they are not already immune.
Dr Dumble said the incubation period lasted about two weeks and people needed to be aware of any symptoms.
The first symptoms were a fever, and one or more of; a runny nose, cough and sore red eyes.
After a few days a red blotchy rash would appear, usually starting on the face before spreading to the body, and lasting up to one week.
People regarded as not immune to measles include:
- Those younger than 45 who have not had two doses of the measles-mumps-rubella (MMR) vaccine, or have not had a laboratory result showing immunity.
- Children over four years of age who have not received their second dose of MMR.
- Infants under 15-months who have not received their first routine dose of MMR.
Dr Dumble said measles could be a very serious illness, with one in three sufferers experiencing complications such as ear infections, pneumonia, bronchitis or diarrhoea.
"On average, one in 10 cases will require hospitalisation," she said.
In 2014 there were 124 cases of measles in Hamilton associated with an outbreak.