New Zealand's Director-General of Health, Ashley Bloomfield, says it's unlikely a Nelson woman caught Covid-19 in the Cook Islands.
The timing of her return from the Cook Islands and her positive test meant it was possible she contracted the illness in the Pacific nation.
However, Dr Bloomfield said this is highly unlikely as there are no cases in the Cook Islands.
He said a Nelson public health officer has been communicating with the Cook Islands Secretary of Health to work through details of the case.
Dr Bloomfield said the virus was likely to have been contracted in New Zealand.
"But whether it happened in another setting during the period after that person arrived back, and so that's more likely. So, I don't think it puts in jeopardy anything that might have happened in the Cooks there."