The number of confirmed swine flu cases in New Zealand has risen by one to five, the health ministry said on Monday, adding that there was no evidence of the virus spreading in the wider community.
The number of probable cases had fallen by one to 12 since Sunday, deputy director of public health Fran McGrath said, while the total number of suspected cases was 69, down 20 from Sunday.
While Mexico's president Felipe Calderon said his country had contained an outbreak there that killed 22 people and infected 568, McGrath said swine flu had not spread into the wider New Zealand community.
"There is still no evidence of community transmission - that means that to date, all of the cases have recently returned from travelling in affected areas or been a close contact of a case," McGrath said.
There were 335 people in isolation or quarantine and being treated with antiviral drugs on Monday, a fall of 25 since the previous day.
The numbers in isolation include people who may have no flu symptoms but have been in close contact with suspected cases.
Although swine flu had so far had only a mild effect on those infected, it could mutate and become more severe, said the health ministry's Darren Hunt.
"Influenza viruses can change and that's another good reason to take a precautionary approach," he told Radio New Zealand.
Trying to prevent the spread was important as southern hemisphere countries such as New Zealand enter the traditional winter flu season.
"We also don't have a perfect handle on what this new virus is like yet, and so we are making a lot of effort to ensure there is no community transmission of it," Hunt said.