The Northland District Health Board has admitted an oversight in not promptly contacting a Ngawha pools where an 11-year-old with measles visited over Easter.
Northland DHB Medical Officer for Health Dr Virginia McLaughlin said she did not contact the manager of Ngawha Springs Hot Pools at the time as the risk was assessed as low and that priority was given to identify the disease's source.
She has since spoken to the pools' manager.
The 11-year-old, a visitor to Northland, did not enter the pools but remained at the entrance on Easter Monday.
But the Northland DHB is now urging anyone who was at the pools between 7pm and 8pm that day to contact its Public Health Unit on 0800 600 720.
"We are not going to close the pools, the time of concern was from 7pm to 8pm on the (Easter) Monday evening only," Dr McLaughlin said.
Parahirahi Ngawha Waiariki Trust, which runs the pools, was not aware of the first measles case when contacted by the Northern Advocate on Monday.
Trust chairman Te Tuhi Robust said his members would seek more information from the Northland DHB about the case.
A 14-month-old from Australia who also visited Northland recently is suspected of carrying the disease.
Both were treated at the Bay of Islands Hospital in Kawakawa last weekend but neither were admitted.
Dr McLaughlin said although the test result for the toddler was not back, the child was in contact with a confirmed measles case in Tauranga and had classic symptoms of the disease.
The Northland DHB is contacting or has contacted more than 49 people who have potentially been exposed to the disease.
She said the Northland DHB's Public Health Unit has provided the pools manager with information they needed to allay any fears the public may have.
"There is no need to check water quality for measles, as this is not relevant. There is no reason to avoid the pools. If people have flu-like symptoms, this applies to any public space setting."
People should use their common sense if they were unwell with flu, measles or gastroenteritis by making choices that didn't put others at risk, she said.
The Public Health Unit is in the process of asking all Northland schools to assess their immunisation register of students and staff, ascertain the level of risk, and provide them with a Measles Fact Sheet they can share with whānau.
Only people who were born before 1969 or have had two measles, mumps, rubella (MMR) vaccinations are considered fully protected.
An estimated 95 per cent of the population must be immunised to prevent recurrent outbreaks of measles.
The present immunisation rate in Northland is 86 per cent and the Northland DHB is urging people to get vaccinated for full protection.
There is no specific antiviral treatment for measles.
Supportive care including rest, good nutrition, vitamin A supplements, painkillers and adequate fluid intake, including hospital care when needed, can help to manage severe complications.