[INTERACTIVE MAP: Map and timeline of swine flu cases]
[CHAT TRANSCRIPT: Questions answered by local expert]
[TRAVEL ALERT: What the CDC wants you to know ]
Some 100 schools were closed, and more might need to be shut down temporarily, President Barack Obama said, declaring, "This obviously is a serious situation." The total confirmed cases in the U.S. rose to nearly 100, with many more suspected.
The Geneva-based World Health Organization sounded its own ominous alarm, raising its alert level to one notch below a full-fledged global pandemic. Said WHO Director General Margaret Chan: "It really is all of humanity that is under threat during a pandemic."
Dr. Richard Besser, acting chief of the Centers for Disease Control and Prevention, said in Atlanta there were confirmed cases in ten states, including 51 in New York, 16 in Texas and 14 in California. The CDC counted scattered cases in Kansas, Massachusetts , Michigan, Arizona, Indiana, Nevada and Ohio.
State officials in Maine said laboratory tests had confirmed three cases in that state, not yet included in the CDC count.
And the Pentagon said a Marine at the Twentynine Palms base in California had been confirmed to be ill with swine flu and was isolated, along with his roommate. A Marine spokesman at the Pentagon, Maj. David Nevers, said the sick Marine was doing well and his condition continued to improve. Nevers said about 30 others who had been in contact with the sick Marine would be held apart for five days as well as to see if they show symptoms.
In Mexico, where the flu is believed to have originated, officials said Wednesday that the disease was now suspected in 159 deaths, and nearly 2,500 illnesses.
Despite calls from many U.S. lawmakers for tightening controls over the Mexico-US border, administration officials ruled out that option.
"Closing our nation's borders is not merited here," said Homeland Security Secretary Janet Napolitano at a mid-afternoon briefing, echoing comments she made earlier in the day while being pressed by senators at a hearing.
She said closing borders or U.S. ports would have enormous adverse economic consequences and would have "no impact or very little" to help stop the spread of the virus.
"This virus is already in the United States. Any containment theory ... is really moot at this time," Napolitano said.
In fact, customs agents have delayed 49 people at the border because of flulike symptoms and 41 have been cleared so far. Test results on the other eight were not complete.
Obama offered "my thoughts and prayers" to the family of a nearly two-year-old Mexican boy who died in Houston, the first confirmed U.S. fatality among more than five dozen infections. Health officials in Texas said the child had traveled with his family from Mexico to Brownsville on April 4 and had been sick for five days before being hospitalized there. He then was brought to Houston where he died Monday night.
Texas called off all public high school athletic and academic competitions at least until May 11 due to the outbreak.
The Senate's top Republican said the spread was a "very worrisome situation and we're all following it very closely." Said Minority Leader Mitch McConnell of Kentucky: "We stand ready to closely work with the administration to protect the American people as this situation unfolds."
Laboratory testing showed the new virus was treatable by the anti-flu drugs Tamiflu and Relenza, and the first shipments from a federal stockpile arrived Wednesday in New York City and several other locations. The government was shipping to states enough medication to treat 11 million people as a precaution. All states should get their share by May 3.
No shortages had been reported -- there was plenty in regular pharmacies, federal health officials said.
A pandemic is an epidemic that has expanded globally. The swine flu has now been reported on four continents.
Germany and Austria became the latest countries to report infections. Germany reported four cases on Wednesday, Austria one case.
New Zealand's total rose to 14. Britain had earlier reported five cases, Spain four. There were 13 cases in Canada and two in Israel.
The disease is not spread by eating pork and U.S. officials appeared to go out of their way on Wednesday to not call the strain "swine flu." Obama called the bug the "H1N1 virus," and other administration officials followed his lead.
"The disease is not a food-borne illness," Rear Adm. Anne Schuchat, CDC's interim science and public health deputy direct, told the Senate Homeland Security Committee.
She said the strain is particularly worrisome because "it's a virus that hasn't been around before. The general population doesn't have immunity from it."
People have various levels of protection against other more common types of flu because they are exposed to it over time, and that protection accumulates. She suggested that some older people might have more resistance to this particular strain than younger people because its traits might resemble outbreaks of decades ago.
Of particular concern were the cases in New York City.
Health officials said the number of confirmed swine flu cases in New York had risen to 51, and tests were under way on the first three probable cases outside New York City.
City Health Commissioner Thomas Frieden said Wednesday all those with confirmed cases are recovering, including a 19-month-old baby and a young woman who were hospitalized.
Two Brooklyn Catholic schools closed Wednesday because of suspected cases. A Queens Catholic school with a large outbreak and a nearby special education school, where about 80 children called in sick, already closed.
Obama said it is the recommendation of public health officials that authorities at schools with confirmed or suspected cases of swine flu "should strongly consider temporarily closing so that we can be as safe as possible."
However, former Kansas Gov. Kathleen Sebelius, on her first full day on the job as health and human services secretary, said school closings cause "a large ripple effect."
"What happens to the parents? Where do those children go? Do you close the day care center if a younger sibling is there?" Sebelius asked at a briefing for reporters.
Obama noted he had asked Congress for $1.5 billion in emergency funds to help build more drug stockpiles and monitor future cases, as well as help international efforts to avoid a full-fledged pandemic, an epidemic that spreads widely across the globe.
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