Viruses from all three patients displayed the same mutation producing the resistance, and officials believe it is a spontaneous mutation, not a recombination with seasonal viruses, many of which are resistant to the drug.
All three viruses were susceptible to the antiviral drug Relenza, known generically as zanamivir.
The WHO is not particularly concerned about the mutations, Fukuda said, because there is no evidence that the resistant virus is spreading.
"The single most important point, at this time, is that we are not recommending any clinical changes to . . . treating patients," he said.
The health agency continues to recommend prophylactic treatment for those exposed to people with a known case of H1N1.
Unlike seasonal flu viruses, the H1N1 virus is continuing to spread largely unabated during the Northern Hemisphere summer.
Outside the United States and Mexico, the greatest spread has been in Britain. Last week, that country's health minister said he expected 100,000 new cases every day for the foreseeable future.
The virus is also spreading throughout the Southern Hemisphere, where the flu season is just beginning. Hardest hit is Argentina, with 2,800 confirmed cases and a death toll that doubled in the last week to 60, the third-highest toll after the United States and Mexico. Chile has had more than 8,000 confirmed cases and 18 deaths. Australia has had more than 6,300 confirmed cases and 13 deaths.
So far, however, the virus does not appear to be changing, and the number of deaths is apparently a reflection of the widespread nature of the disease.
Africa has been the last continent to see an outbreak, and the virus' presence has now been confirmed in 12 countries there, Fukuda said.
The continued spread of the virus to developing countries will severely tax the United Nations, which will need more than $1 billion this year alone to combat the pandemic, Secretary-General Ban Ki-moon said Monday.
He said the agency has not been receiving as much money for the pandemic as it had hoped.
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thomas.maugh@latimes.com
