Avian flu has the potential to be a major crisis, and top government and public health officials are planning for the worst. However, almost without exception, they all say the worst-case scenario -- easy transmission from human to human -- is unlikely, but still possible.
Here are two key facts to help put the virus in context:
Right now, this is a virus that primarily affects birds. More than 200 million birds have died or been killed, while 97 humans have died worldwide. Each year in just the United States alone, 36,000 people die from seasonal flu.
In China, the disease is widespread among birds. The World Health Organization has confirmed just 15 infections and 10 deaths among humans in a population of 1.3 billion people -- a rate of one case per 86 million people and one death per 130 million.
Here is what some prominent officials and health experts have said about bird flu:
"If the virus were to develop the capacity for sustained human-to-human transmission, it could spread quickly across the globe."
"Our country has been given fair warning of this danger to our homeland -- and time to prepare."
Dr. Anthony Fauci, director, National Institute of Allergy and Infectious Diseases at the National Institutes of Health
"Americans need to know that it is a threat, a real threat. It is an unpredictable infection, a pandemic flu, which really means a kind of flu to which the American public or the whole world, the global population has not been exposed to before. It is very different from the seasonal flu."
"So you have to walk that balance of being prepared for something that may not come this year, may not come next year, but sooner or later knowing the history of how pandemic flus evolve over a period of time, over decades and decades, it will occur. So we need to be prepared."
Robert Webster, world-renowned virologist at St. Jude Children's Research Hospital, consultant to the World Health Organization and the National Institute of Allergy and Infectious Diseases
"About even odds at this time for the virus to learn how to transmit human to human. As the virus continues to expand its range as it's continuing to do into Africa, India and so on, I think it's got about a 50-50 chance of acquiring those characteristics. It's done so before, why not this time?"
"What should the average person do? The average person should be prepared to live in their family unit for three months. You have to have food, dried food, resources to live for 3 months in your unit. And so that's the maximum we can do."
Dr. Dick Thompson, World Health Organization spokesman on communicable diseases
"It's very unusual that a virus with pandemic potential actually appear. So, that has us concerned from the beginning. But have we seen any change in the last two years that makes us think that this is on the edge of mutating into a pandemic strain? … Definitely not."
Dr. John Treanor, professor of medicine, Infectious Disease Unit, University of Rochester Medical Center
"If nothing else, [flu in U.S. birds] may present a very severe problem for agriculture in the Western Hemisphere."