One-in-five report flu symptoms

Margaret Drury hangs a poster at Hawkes Bay Hospital advising patients how to help stop the spread of swine flu. Photo / Hawke's Bay Today

More than a fifth of adults may have had an influenza-like illness in the first months of the swine flu pandemic, a survey indicates.

Nearly half those reporting flu symptoms said they had been "quite" or "very" unwell and 4 per cent said they had had swine flu, according to the survey results. The telephone poll of 600 adults was done in Canterbury by Opinions Market Research for the region's Civil Defence Emergency Management Group.

It is the first publicly reported phone poll to try to assess the extent of influenza infection since the swine flu pandemic began in late April.

A public health specialist, Associate Professor Michael Baker, of Otago University at Wellington, said 22 per cent reporting flu-like symptoms in a telephone survey was about what might be expected.

"You might find that in any one year. But you can't convert that to a valid measure of influenza prevalence. It's great that they have taken the initiative to look at the impact of the pandemic ... it's really a blind spot in our knowledge."

But he said telephone surveys on flu produced higher figures than the real number of cases.

Even when influenza-like illness was identified by doctors, such as in the sentinel-GP reporting system used to track influenza each flu season, only a quarter of those whose throats were swabbed turned out to have influenza infection. The rest mostly had some other respiratory virus.

On average, 10 per cent of the population catch influenza each flu season, which runs from May to September.

Dr Baker said possibly half of those who have had flu this season would have had the pandemic virus. "The pandemic virus is gradually becoming dominant."

He said the best way to determine the prevalence of swine flu would be to do blood tests on a sample of the population, after the pandemic ended, and find the proportion who had antibodies against the virus.

The Ministry of Health reported yesterday that 2810 confirmed cases of swine flu had been notified so far, but the figure is now regarded as meaningless because only a minority of potential cases are being tested. The official death toll remains 13.

The survey also asked about levels of preparedness, awareness of the pandemic and its social impact. It showed most people counted on friends and family for help.

HOW MUCH FLU?

Survey of 600 adults questioned between June 30 and July 11
* 22 per cent said they had had flu-like symptoms since late April.

Of those:
* 16 per cent had been very unwell; 38 per cent quite unwell.
* 4 per cent said they had had swine flu.