Two of the patients were men aged 59 and 86 and the other was a boy aged seven. All three had reportedly been in contact with dead chickens and were being treated in an isolation ward at Phichit Hospital.

Pending the results of laboratory tests for evidence of the bird-flu virus, doctors said the three patients were not allowed visitors.

Livestock officers in the province were stepping up disinfection of sites where irregular poultry deaths were reported. Hundreds of such deaths have recently been reported in the province.

Meanwhile, deputy chief health officer for Chiang Mai, Surasing Wisarutarat, warned the public not to cook dead chickens, no matter how they died.

"The group we're most concerned about is immigrant workers," he said. "They are most likely to opt for dead chickens and risk contracting bird flu."

Despite numerous reports of irregular poultry deaths in many areas, particularly the North and Central provinces, the Department of Livestock Development insists that no avian flu has been detected so far.