Health officials are becoming increasingly concerned that swine flu, which has killed 180 people worldwide, could become resistant to Tamiflu.
Those fears follow confirmation that normal winter flu strains were no longer susceptible to the antiviral drug.
More than 40 people have tested positive for swine flu since Friday, pushing total infections to 258, the Ministry of Health said yesterday.
However, ministry officials have said the actual number of people infected was likely to be "in the thousands" as doctors had stopped testing every patient.
A 30-year-old woman remained in a critical condition in Wellington Hospital's intensive care today, a hospital spokesman told NZPA. Those diagnosed with the H1N1 strain had been prescribed Tamiflu.
But Environmental Science and Research virologist Sue Huang, head of the World Health Organisation national influenza centre in Upper Hutt, told The Dominion Post scientists feared swine flu could mutate with a Tamiflu-resistant strain.
All 18 seasonal influenza type A strains tested so farthis year had been Tamiflu-resistant.
"Viruses are notoriously unpredictable ... if there was mixing of the novel virus with other A(H1N1) strains circulating, such as in a person infected with both strains, the novel virus could take on resistant characteristics." The ministry was now stockpiling another antiviral drug, Relenza.
Meanwhile, Auckland will today follow the lead of Wellington and Christchurch and begin focusing on managing swine flu cases rather than trying to contain the virus.
And in Christchurch last night the flu centre extended its opening time by six hours a day to cope with the number of people referred to it with flu symptoms.
Ministry director of public health Mark Jacobs said most people who contracted swine flu would only be mildly to moderately ill and they should be able to care for themselves at home.
"However, a person should seek medical care if they develop flu and they have other significant health problems, or if they become more seriously ill (for example, if they experience shortness of breath)." Only the people most vulnerable to developing serious complications, or those with serious cases, would be swabbed and tested for swine flu.
