There is no vaccination for the swine flu strain, which has elements of pig, bird and human strains. But officials said they have ramped up medical surveillance around the country and, as part of the emergency declaration, freed up state and federal resources for prevention. Officials also emphasized the importance of individual care and good hygienic practices.
"Even if this outbreak is a small one, we can't anticipate we won't have follow-up outbreaks," U.S. Homeland Security Secretary Janet Napolitano said.
A different scenario is unfolding across the border in Mexico. While authorities hunt for the source of the swine flu outbreak, the country is under lock down. Schools, museums, parks and even churches in Mexico City have been shut down by the government. A leading business group estimates that canceled events and closure of establishments to prevent the spread of swine flu is costing Mexico City at least $57 million a day.
"I haven't been out for days," said one woman, who only left to bring her baby to the doctor for a routine vaccination.
More than a thousand people countrywide have been infected. The government has advised people to stay home and indicated that those infected by the virus could be isolated. In the country's deserted capital, public events were cancelled for the next week or so. Sales of masks have soared as people try to prevent themselves from the potentially deadly disease.
Mexican officials are hoping the 10-day shut-down will be enough to cover the two-day incubation period and the seven-day recovery of anyone who has the virus.
Mexico's first suspected case of the swine flu was detected in the remote farming village of La Gloria, where 5-year-old Edgar Hernandez contracted the disease nearly one month ago, authorities say.
"The most likely way that this young boy got the infection was from another person who had been in contact with the pigs," said Dr. Kathryn Edwards of Vanderbilt Medical Center.
More than 800 people in the town of 2,000 were infected, authorities say, but no deaths were reported. It took seven days for Mexico to confirm its first cases of swine flu, according to World Health Organization estimates.
Officials say it's still too early to determine how the disease spread from La Gloria into a global health emergency.
"It's a new virus, new virus combination, it does transmit from person to person and we already know it causes fatalities so we already have all the makings of a possible pandemic," Irwin Redlener of Columbia University's Mailman School of Public Health said.
But Dr. Nancy Cox of the CDC has said she believes the earliest onset of swine flu in the United States in this current outbreak happened March 28.
A quarter of the 50 million doses of Tamiflu stockpiled by the U.S. government has been released and the Obama administration has declared a public health emergency to free up the medicine and federal help to the states who need it.
But pharmacies in several states have been flooded with phone calls from concerned customers.
"Our first phone calls were doctors asking if we had Tamiflu," New York City pharmacist Yvonne Zampitella said. "They were prescribing it for their patients and family members."
Symptoms of the swine flu are similar to the regular flu, health officials say, including aching muscles, fever and fatigue. The virus appears to be responsive to medication.