It's more likely a New Zealand woman contracted the Zika virus through sex than by being bitten by a mosquito in this country, a specialist in infectious diseases says.
The Ministry of Health has revealed a man who visited a country where the virus is active has tested positive, and so has his partner, who has not been to any Zika-affected country.
Both suffered only mild symptoms and have fully recovered.
The Ministry said the virus could have been transmitted through unprotected sex, or the woman could have been bitten by an infected mosquito brought into the country in her partner's luggage.
But Auckland University infectious disease specialist Siouxsie Wiles told Morning Report the mosquito theory was improbable.
She said it was most likely the virus was sexually transmitted, as there had been similar cases overseas.
"It would've had to have been a female mosquito, because they're the only ones that transmit the virus...I think that's the least likely of the explanations considering that sexual transmission does happen."
However, that didn't mean the virus could take hold in New Zealand, Dr Wiles said.
She said rather than only having cases occurring in people who had visited infected countries, there could be clusters of cases through secondary transmission, depending on the number of sexual partners people had.
"And we don't have the mosquitoes to then pick it up from the people who are infected and then transmit it further. So it should stop with the secondary cases."
Dr Wiles said it was not known if the Zika virus had the same effect with secondary transmissions.
It was important that people who had been to infected countries practised safe sex including using condoms for up to six months, she said.
75 Zika cases confirmed
The total number of people in New Zealand treated for Zika for this year has reached 75.
While most cases are undetectable or cause mild symptoms such as low fever or joint pain - the virus has been linked to microcephaly, a severe birth defect.
The latest Institute of Environmental and Scientific Research figures show there have been 71 confirmed cases of Zika in New Zealand, while another four are considered likely.
The figures show of those affected 49 were exposed to the disease while travelling in Samoa, a further 20 in Tonga and a handful were in American Samoa.
Only one case of the virus has been contracted in New Zealand.
In 2014 there were 57 Zika notifications, compared to only six last year.