MEXICO CITY - Fears of a global swine flu pandemic grew with new infections in the United States and Canada on Sunday, and millions of Mexicans hid indoors to avoid a virus that has already killed up to 81 people.
While the only deaths have been in Mexico, the flu is spreading with 20 cases in the United States and six in Canada, and possible cases as far afield as Europe, Israel and New Zealand.
Offering a glimmer of hope in Mexico, President Felipe Calderon said most of the roughly 1,300 people in the country suspected of having the flu have been given a clean bill of health.
The United States declared a public health emergency and a top official at the Centers for Disease Control and Prevention, or CDC, said she feared there would be deaths in the United States as the new strain of flu spreads.
The Mexican capital, one of the world's biggest cities, slowed to a snail's pace as millions of residents stayed at home, fearing infection. Many who ventured out wore masks.
"This is the first time I've left the house in two days. I had to get some air," said Juan Casiano, a 39-year-old office worker, walking briskly through a city park.
The Roman Catholic faithful listened to mass on the radio rather than go to church, and baptisms and confirmations were cancelled. Professional soccer games were played in empty stadiums, bars were closed and cyclists stayed off the road in the normally chaotic city of 20 million people.
Mexico's retail and leisure sector faces a hole in takings as shoppers and diners stay home next week. Mexico City Mayor Marcelo Ebard said public closures could last 10 days.
Finance Minister Agustin Carstens said the flu's impact would be "transitory," but the peso currency, already weakened by the economic crisis, fell nearly 3 percent in electronic trading on Sunday night as traders reacted to the scale of the flu crisis.
The World Health Organization has declared the flu a "public health emergency of international concern" that could become a pandemic, or global outbreak of serious disease.
A pandemic would deal a major blow to a world economy already suffering its worst crisis in decades, and experts say it could cost trillions of dollars.
A 1968 "Hong Kong" flu pandemic killed about 1 million people globally.
U.S. deaths expected
Mexico did not raise its death count over the weekend, but there were worries that fatalities could surface elsewhere.
"I do fear that we will have deaths," the CDC's Dr. Anne Schuchat said. She told reporters officials were preparing for the illness' possible spread beyond the 20 cases confirmed in the United States.
Eight schoolchildren in New York were confirmed as having caught the swine flu virus, although like other cases reported outside Mexico they were relatively mild.
Officials said they would release a quarter of the U.S. stockpile of the antiviral drugs Tamiflu, made by Roche, and Relenza, from GlaxoSmithKline. Both have been shown to be effective against the new swine flu.
Flu is characterized by a sudden fever, muscle aches, sore throat and dry cough. Victims of the new strain have also suffered more vomiting and diarrhea than is usual with flu.
Although it is called "swine flu" there is no evidence any of the cases stemmed from contact with pigs.
Health officials say they do not understand why deaths have been reported in Mexico but nowhere else. "I think right now it is really premature to say the disease is different in Mexico from here," Schuchat said.
The outbreak has snowballed into a major headache for Mexico, already grappling with a violent drug war and economic slowdown, and has become one of the biggest global health scares in years.
"It's very frustrating. If you go out, you get mugged -- or you get some weird virus," complained Cynthia Gonzalez, 32, a sales manager who spent most of the weekend at home.
"We wanted to go out but we have a baby so we wanted to be sure it was safe. The doctor said it was okay as long as we're not in enclosed spaces or with infected people," she said.