Queenstown Airport has been identified as the place where two adults and a 13-month-old baby contracted the notifiable disease measles.
Three cases had since been reported — in Queenstown, Wanaka and Christchurch — prompting both the Southern and Canterbury District Health Boards and Queenstown Airport to put out an alert.
"At this time the common place of exposure for all three cases is Queenstown Airport, where all three are likely to have been in contact with an unknown infectious case on 21 or 22 March," the report said.
The unknown infectious person may have had a relatively mild illness and now be fully recovered and anyone else exposed to that person would be at the end of the maximum incubation period, and unlikely to get sick.
However, people who were not immunised and who may have been exposed to any of the three subsequent South Island cases would most likely become ill between April 10 and April 20.
Measles is a highly infectious viral illness, spread through coughing and sneezing. It generally affects less than 100 people a year in New Zealand.
None of those in the three South Island cases were immunised against measles and those who had been in close contact with them had been identified and would be followed up.
SDHB medical officer of health Dr Marion Poore said it was important people with measles symptoms did not visit their GP or after-hours clinic, but first phoned their family doctor for advice, to limit exposure to other people.
"People are infectious from five days before the onset of the rash to five days after the rash starts and should stay in isolation during this time," she said.
Many of New Zealand’s cases came from arriving travellers who may have been in countries lacking vaccination, she said.
Symptoms started with a dry cough, runny nose, temperature above 38.5degC and "flu-like" symptoms, before a rash started on day four or five, usually moving from the face, to chest then arms.
Dr Poore said people with up-to-date vaccinations would be protected, but if people were unsure they should check with their doctor.
She said the best protection was to have two MMR (measles, mumps, rubella) vaccinations which gave more than 95% protection.
Queenstown Airport manager communications and community Jen Andrews said medical advice had been shared with staff and the situation monitored.
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