The Northland District Health Board has issued a public alert after a woman was hospitalised with measles at the weekend.
The woman, who was unvaccinated, was admitted to intensive care on Saturday, and is now in a stable condition. She was admitted with encephalitis and seizures.
She had returned to New Zealand from the Philippines in early May, and became ill two weeks later.
The DHB is warning that she may have infected others, and it is following up on more than 100 contacts.
Medical Officer of Health Dr Virginia McLaughlin said there is also a low risk for people who were at Kensington Stadium in Whangārei on Friday 17 May. She said anyone who was at the stadium that night between 6.20pm and 8.30pm should contact the Public Health Unit on 0800 600 720.
"It was a netball match between two teams, one from Whangārei and one from Dargaville. We've managed to contact the people from both the teams. So it's just really a matter if anyone else was in the stadium at that time and it would be great if they could make contact with us so that we can assess their risk a bit more."