Health authorities estimate a measles outbreak in Auckland is at its peak, but are still advising the public to be wary.
There are four confirmed cases of the virus, with 48 people in quarantine, after an infected man ignored medical instructions and visited public areas, including SkyCity Casino.
Dr Richard Hoskins from the Auckland Regional Public Health Service says it's putting a strain on the system.
"What we do now is try and stop it any further which is why we get in contact with anyone who may have been in contact with those people."
Dr Hoskins says it's possible to catch measles by being indoors and breathing the same air as an infected person.
Medical Association chair Dr Stephen Child says air can remain infected for hours.
"Some fascinating studies show that if someone has measles and walk out of the room it's still in the room for up to two hours after they leave the room."
He added that it's never too late to get immunised.