A third of the people known to have been near a netball player in Northland who became seriously ill with measles don't have immunity to the disease, health authorities say.
The young woman was admitted to Whangarei Hospital on Saturday with seizures and encephalitis, or swelling of the brain. Her condition remains stable.
She was not vaccinated and developed symptoms of measles about two weeks after returning from a visit to the Philippines in early May, Northland District Health Board said.
Medical officer of health Dr Virginia McLaughlin said they had been in touch with all the close contacts they were aware of.
"We've managed to contact about 100 people and currently we've got 36 people on that list that we know don't have immunity to measles so we're contacting them every day to see if they develop symptoms.
"We keep a close eye on them and if they do happen to develop measles it will be easy for us to manage that rather than having someone out in the community who we're not aware of potentially infecting a whole other group or groups of people."
Dr McLaughlin and are appealing for anyone else who was near the player at the match at Kensington Stadium on Friday 17 May between about 6.20pm and 8.30pm to contact the Whangarei public health unit on 0800 600 720.
"It sounds as though she didn't complete the game so certainly it would appear she was unwell at that time."
Northland District Health Board said it was the fourth case of measles in Northland this year, and the third to have originated from outside the region.
In 2019 there have been outbreaks of measles in Canterbury (now declared over), Auckland and Bay of Plenty. Cases have also been reported in the Waikato, Lakes, Capital and Coast, and Southern DHB areas.
In Auckland about half those who had measles had ended up in hospital, many more than usual.
There have been 149 confirmed cases reported nationally up to 22 May, with another 44 cases under investigation