Swine flu has become the most prevailing flu virus in New Zealand and some emergency departments are struggling to manage.

Hospital admissions for winter illness are increased although numbers were down compared to last year's outbreak. Almost 1900 people visited hospitals in the week with flu-like symptoms.

An emergency department estimates upto two-thirds of patients have been given Tamiflu or its generic equivalent, oseltamivir.

Many Auckland schools reported about one child per class had been sick each day, and the city's hospitals said they were running near capacity.

Last year, many people with the flu were kept away from hospitals. But this year, people with flu-like symptoms have flooded emergency departments - and staff numbers are down with many having caught the flu themselves.

Swine flu or Influenza A H1N1 09 became a pandemic last year. Non-influenza viruses circulating New Zealand include rhinovirus and respiratory syncytial virus, which is highly contagious and demands isolation at hospitals.

Waikato Hospital clinical microbiologist Chris Mansell said swine flu was currently the only influenza strain circulating New Zealand and the laboratory tests for patients in Waikato have found up to one in 10 patients with a winter illness had influenza, with swine flu detected.

The Ministry of Health said tests showed swine flu was the predominant strain this year. Swine flu is the year's biggest threat among winter illnesses, but it is already well established and therefore less likely to explode.

The Ministry of Health estimates more than a million New Zealanders - almost a third of the country has been exposed to swine flu and has become immune to the strain, including those who received a vaccine.

Dr Jarman said that pregnant women with flu-like symptoms had a high chance of contracting a severe disease and were strongly urged to get immediate advice from their doctor

But influenza usually spikes with a sudden upsurge spanning about two weeks, and this could still be coming.