The first American citizen has died from the swine influenza A-H1NI virus known as "swine flu", and the number of confirmed cases in the United States has surged to 642. The victim was a 33-year-old woman from Texas who officials say had other chronic health conditions.

A congressional foreign affairs subcommittee held a hearing Wednesday on the national and global implications of the H1N1 flu epidemic.

Anne Schuchat of the Centers for Disease Control and Prevention told the hearing that U.S. health officials have moved with impressive speed to isolate and study the new virus. "We have been able to move within two short weeks to identify this novel virus, understand the complete genetic characteristics and compare the genetic composition of specimens from U.S. patients to others around the globe to watch for mutations," he said.

Schuchat said these efforts put the United States in a good position to produce a vaccine. "We have initiated steps so that should we need to manufacture a vaccine, in terms of the U.S. government's role, we can work towards that goal very quickly," he said.

Dr. Dennis Carroll, a special adviser on pandemics with the U.S. Agency for International Development said investments to prevent an avian flu epidemic helped lay the groundwork for the quick response to the H1N1 virus. But Dr. Carroll also warned of a broader and disturbing global trend relating to new diseases and animals.

"In fact 75 percent of all new emergent diseases that have emerged in the past 50 years, their origin are animal," he said.

Carroll said the U.S. Agency for International Development is working in cooperation with other agencies to set up a global early warning system to detect and respond to brand new strains of virus and diseases across the world.

Anthony Fauci of the National Institutes of Health cautioned people will not have immunity to new viruses. "Influenza virus are inherently unpredictable anyway. When you have a virus that you have never had experience with before, that compounds the unpredictability," he said.


Fauci and Schuchat both warned that Americans should be prepared for the potential return of the H1NI virus later this year, possibly in a more severe form.