http://www.nytimes.com/2006/05/24/world/asia/24birdflu.html?_r=1&oref=slogin INDONESIA, May.24 (NYTIMES): Reacting to the death on Monday of an Indonesian man, the World Health Organization 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 W.H.O. 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. Six more family members who were at the barbecue fell sick in the first week of May. Five of them, including the 10-year-old, died in the second week of May; only one, the hostess's 25-year-old brother, recovered. Thirty-three other people in Kubu Sembilang who had contact with the family have been quarantined or have been treated with Tamiflu, an antiviral drug, Ms. Cheng said. The W.H.O. assumes that the incubation time for bird flu in humans is 7 to 10 days, longer than that of regular flu, she said. Henry L. Niman, who runs recombinomics.com, a Web site tracking the genetics of flu cases, argues that the incubation period is closer to the two to four days of regular flu, so the boy may have been infected by another family member, meaning that the virus might have made three consecutive human-to-human jumps. But Ms. Cheng said the health agency's "working hypothesis" was still that it had jumped only twice. An Indonesian health official, according to local news reports, said the boy's father had run away after falling ill and had been treated with Tamiflu. He was later found in the village again but refused treatment. Ms. Cheng said the village had "not been as cooperative as we'd like." Recalling outbreaks of Ebola in which African villagers had been terrified at the sight of foreign doctors arriving in hoods and white overalls, she said she thought that the W.H.O. team had worn civilian clothes, and put on masks only when talking to sick patients.