Reacting to the death on Monday of an Indonesian man, the World Health Organisation said yesterday that the case appeared to be the first example of the avian flu jumping from human to human to human.

But the health agency quickly cautioned that this did not necessarily mean that the virus had mutated into a strain that could start a pandemic by jumping rapidly between people as ordinary flu does.

It is a “definite possibility” that the virus jumped more than once inside a family cluster, said Maria Cheng, a spokeswoman for the WHO in Geneva. Although a second jump sounds alarming, “It doesn’t look like the trend has changed,” she said. “Each case was in very close contact with the previous one.”

In the past there have been at least three cases of suspected human-to-human transmission of the A(H5N1) strain of bird flu; all were between family members who spent hours in close contact and would have breathed in large amounts of virus-contaminated droplets. The virus is known to attach itself to receptors deep in the lungs, not in the nose and throat as seasonal flu does.

The man who died was 32 and became sick on May 15. He is believed to have caught the flu while caring for his 10-year-old son, who died of the disease on May 13.

The boy attended a family pork roast in the village of Kubu Sembilang in northern Sumatra on April 29. The hostess, a 37-year-old woman, had become sick on April 27 and was coughing heavily, and several family members slept in her small room, the health agency said. She died May 4 and was buried without any tissue samples being taken; she is presumed to have spread the flu only because of her symptoms.

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