Outbreaks Show Bird Flu Virus Is Changing

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In the Indonesian report, led by epidemiologist Dr. Timothy Uyeki of the U.S. Centers for Disease Control and Prevention, researchers found that H5N1 affected some patients more severely than others, suggesting that there are genetic factors influencing patient vulnerability. They also noted that certain drugs, such as oseltamivir (Tamiflu), could help fight the predominant Indonesian strain, but these drugs are only effective when given a day or two after infection. That's probably too early for most patients, however.

"In the countries that have reported human H5N1 cases, patients generally do not seek medical care early in their illness," Uyeki explained. "They usually present for medical care when their illness is advanced, e.g., they have pneumonia, and therefore they are not able to receive early oseltamivir treatment."

In their commentary, Webster and Govorkova noted that the number of documented human cases of H5N1 infection is rising worldwide. A total of 251 cases have been recorded globally since 1997, they said, and "by mid-August, 97 humans had been infected in 2006 -- the same number as in all of 2005."

No definite case of human-to-human transmission has yet been reported, suggesting that "the current H5N1 virus is apparently not well 'fitted' to replication in humans," the two experts wrote. However, "the intermittent spread to humans will continue, and the virus will continue to evolve," they added. "Clearly, we must prepare for the possibility of an influenza epidemic."

Siegel believes this kind of language can be misleading.

"We don't know enough about H5N1, and the science hasn't evolved to the point where we can predict when an epizoonotic problem -- a disease that has killed a lot of birds -- is going to start killing a lot of humans," he said.

And, while reports do suggest a rise in human cases over time, Siegel noted that, prior to 1997, no one was keeping close tabs on the epidemiology of H5N1. "I think there may have been previous clusters that might have gone unreported because of a lack of attention -- they may have been misdiagnosed as other kinds of flu," he explained.