The head of the Centers for Disease Control and Prevention said Sunday that the human swine influenza that has killed scores in Mexico but so far infected only a handful of Americans will spread further inside the United States before the virus is under control.
"I expect, as we continue to look for cases, we're gong to see a broader spectrum of the disease," said Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention (CDC) during a White House news conference Sunday. "Given the reports out of Mexico, I would expect that over time we're going to see more severe disease in this country."
At least 20 confirmed cases of swine flu have been reported in recent days in California, Texas, Kansas, Ohio and New York, with those infected ranging in age from 9 to 50 and older.
On Sunday, the CDC confirmed the flu had infected eight students of a New York City high school. The school announced Sunday on its Web site that it will be closed Monday and Tuesday.
A similar or identical flu strain in Mexico has killed up to 81 people and likely sickened 1,324 since April 13.
No deaths or serious illness connected with the flu have been reported in the United States.
Dr. Besser said that this strain of flu -- like most new flu viruses -- is extremely difficult to predict and that the CDC's response will change accordingly. He said the agency's Web site will post daily updates on the spread of the flu.
"We expect that we'll be changing our recommendations over time based on what we learn," Dr. Besser said.
No travel restrictions to Mexico have been implemented by the U.S. government, although the CDC has posted travel warnings on its Web site regarding the flu outbreak in Mexico.
"We're going to continue to evaluate the situation in Mexico, and if need be, we will increase the warnings based on what the situation warrants," Dr. Besser said.
The State Department as of Sunday had not issued travel advisories to Mexico, but Obama senior adviser Valerie Jarrett said the administration wouldn't rule out the possibility if the flu outbreak worsens.
"Let's just put it this way: The president is taking this very seriously," Ms. Jarrett said on CNN's "State of the Union" on Sunday. "He has assembled his teams from the Centers for Disease Control and Homeland Security. He has been briefed regularly. And he has asked them to speak to the American people and give the appropriate counsel later today."
Ms. Jarrett said the president did not get sick during or after his trip to Mexico this month.
Persons legally traveling to the United States from Mexico will be allowed entry provide they don't show symptoms of the flu virus, said Homeland Security Secretary Janet Napolitano at the White House news conference. Travelers who do exhibit symptoms of the virus will be quarantined.
"We have implemented passive surveillance protocols to screen individuals who may arrive at our borders," she said.
In response to the spread of the flu, the Health and Human Services Department (HHS) on Sunday declared a "public health emergency" in the United States -- a standard procedure that allows money and resources to be made immediately available for state governments to combat the flu.
As an additional precaution, Ms. Napolitano said, a quarter of the 50 million treatments of anti-viral vaccine in the CDC's Strategic National Stockpile will be made available to state governments.
Ms. Napolitano added that the public must do its part to contain the spread of the flu, such as routine hand washing and staying home if sick.
"The government can't do this alone -- we need everybody in the United States to take some responsibility," she said.
White House spokesman Robert Gibbs said Sunday that the spread of the flu is a "great concern" for the administration and that federal agencies, including Homeland Security, Health and Human Services and the CDC, are briefing President Obama every few hours on the situation.
"It's serious enough to be a great concern to this White House and to this government," Mr. Gibbs said. "We are taking proper precautions to address anything that happens. It's not a time to panic."