WASHINGTON AND LOS ANGELES — Federal officials declared a public health emergency Sunday as eight cases of swine flu were identified in New York and one was announced in Ohio, bringing the U.S. total of confirmed cases to 20.
In a briefing at the White House, the acting head of the Centers for Disease Control and Prevention, Dr. Richard Besser, warned Americans to prepare for a widespread outbreak, yet urged the public to remain calm.
Also Sunday, Homeland Security Secretary Janet Napolitano said the government would release a quarter of its 50-million-unit strategic reserve of antiviral medications, which combat the disease in infected patients, to states where outbreaks had occurred.
Canadian officials, meanwhile, said four cases had been confirmed in Nova Scotia and two in British Columbia, marking the first time that this particular strain had appeared north of the U.S. border. All six Canadian cases were mild, like those in the United States.
Several other countries have reported influenza-like illnesses that they suspect may be swine flu in travelers returning home from Mexico, but as of Sunday evening, none of them had been confirmed.
Nonetheless, many nations moved quickly to limit the disease's spread, in many cases appearing to be near panic. Some, such as Poland and Venezuela, warned against traveling to the United States or Mexico. Others, such as Russia and Brazil, began screening some incoming international air travelers for signs of high fever.
China, Russia and Taiwan said they would quarantine returning passengers with flu symptoms.
In Mexico, Health Secretary Jose Angel Cordova said almost two dozen more deaths had occurred from influenza overnight, bringing the death total to 103. At least two of the new cases were confirmed as swine flu, for a total of 22 confirmed swine flu deaths. It is not clear how many of the others were caused by the virus.
Of the more than 1,600 suspected flu cases in that country, the Mexican government has said most are probably linked to other strains of the flu or respiratory diseases, not the new strain of swine flu.
On NBC's "Meet the Press," White House Press Secretary Robert Gibbs said swine flu was "serious enough to be a great concern to this White House and to this government." He added that President Obama was receiving frequent updates on the situation.
"We are taking the proper precautions to address anything that happens," Gibbs said. "It's not a time to panic."
Napolitano said the emergency declaration was a routine move to ensure that the government was prepared "in an environment where we really don't know, ultimately, what the size or seriousness of this outbreak is going to be."
It seemed certain, however, that the number of swine flu cases -- mild or otherwise -- would rise. "As we continue to look for cases, we are going to see a broader spectrum of disease," Besser said. "We're going to see more severe disease in this country."
Because of the situation in Mexico, "I do feel that we will have deaths here," Dr. Anne Schuchat of the Centers for Disease Control and Prevention said at a separate news conference. She's the interim deputy director for science and public health programs.
Besser said the CDC had isolated the swine flu virus and prepared a "seed stock" for the manufacture of a vaccine but would not distribute it to pharmaceutical companies until the situation became more severe. Manufacture of a new vaccine will require months.
Public health officials cast the various moves as aggressive but precautionary, and they counseled calm.
The eight confirmed cases in New York involved students at St. Francis Preparatory School in Queens. City officials had said Saturday that the virus involved was probably swine flu, and that was confirmed overnight by researchers at the CDC. Some of those students had taken a spring break in Mexico.
Flu-like symptoms have been reported in some of the parents, but causes have not been confirmed.
Officials also tested children at a New York day-care center where illness had been reported, but those tests came back negative.
The new case in Ohio is a 9-year-old boy in Lorain County. He has a mild case of the disease and is recovering at home.
Previously announced cases included two in Texas, two in Kansas and seven in California's Imperial and San Diego counties. All the cases were mild, and the victims have recovered.
The Nova Scotia Department of Health Promotion and Protection said Sunday that four cases had been confirmed in Windsor, Hants County, in eastern Canada. The four victims were students who had recently traveled to Mexico. None of them have been hospitalized.
Two teenage boys in British Columbia in western Canada were also confirmed to have swine flu. Both had mild cases, which were identified as swine flu only because their doctors heeded government calls to perform tests on flu victims who had traveled out of the country.