Swedish research shows many bird flu cases missed

The dreaded bird virus H5N1 could have infected far more people in Asia than statistics have so far shown, say researchers at Stockholm's Karolinska Institute. The symptoms of the disease are often so mild that people have not realised that they have the influenza.

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This surprising conclusion came from a new study led by the Institute's Anna Thorson and carried out with Vietnamese scientists.

Researchers investigated the health of 45,478 randomly selected people in Bavi district, an area where there had been several outbreaks of bird flu.

Many of those people were from households which kept their own poultry and of those a quarter, 11,755 people, reported having had sick or dead birds.

In total, 8,149 people said that they had had "flu-like symptoms". Anna Thorson and her colleagues believe that the majority of cases were normal flu or similar illnesses. But, they say, 650 to 750 cases were probably bird flu.

"That is the most credible explanation. That suggests that there was a previously unknown, milder variant of bird flu," said Thorson to TT.

The study just encompassed one district in Vietnam and Anna Thorson declined to speculate on a possible total number of cases in the country. But if the results are matched elsewhere, the true figures are far greater than those which have been made official: 87 cases, of which 38 have resulted in death.

"Everyone has accepted that bird flu is an exceptionally unpleasant disease with high mortality. But maybe that is not the case. Maybe it's more like normal flu in its character when it affects humans," she said.

Thorson emphasised that the results must first be verified against microbiological studies.

But the research appears to have supported the theory that close contact with sick or dead birds is crucial of the disease is to spread to humans. The most important factor in the fight against bird flu is good control of poultry stocks.

The study was published in the scientific journal Archives of Internal Medicine.

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TT/The Local