MEXICO CITY — Mexico reported three new deaths from the swine flu epidemic Saturday and urged citizens not to let their guard down against a virus that has killed 19 in people in Mexico and is spreading across Asia and Europe.
Health Secretary Jose Angel Cordova said Mexico's confirmed swine flu cases jumped to 473, including the 19 deaths. The previous death toll in Mexico was 16. A Mexican toddler also died in Texas days ago, for a worldwide total of 20.
Mexico's last confirmed swine flu death occurred Wednesday, Cordova said. However, he said there were 11 cases of people suspected to have died from the virus in the last 24 hours. The alarming news came after the epidemic's toll in Mexico appeared to be leveling off.
Cases outside Mexico suggested the new swine flu strain is weaker than feared, but governments moved quickly anyway to ban flights and prepare quarantine plans. Experts warned the virus could mutate and come back with a vengeance.
In the first known reported case of the new, mutated virus infecting another species, pigs in the province of Alberta have become infected and are under quarantine. They apparently got the virus from a Canadian farm worker who recently visited Mexico and got sick with swine flu, Canadian officials said Saturday.
They told a press conference in Ottawa that the pigs do not pose a food safety risk, adding that the traveler recovered from the swine flu and the pigs are "well on their way to recovery." The outbreak occurred on a single farm, where about 10 percent of 2,200 pigs showed a fever and loss of appetite. No pigs have died from the virus, officials said.
The U.S. Centers for Disease Control and Prevention said it's too early to declare victory.
The World Health Organization also decided against a full pandemic alert, but that doesn't mean people can relax, said Dr. Mike Ryan, WHO's global alert and response director.
"These viruses mutate, these viruses change, these viruses can further reassort with other genetic material, with other viruses," he said. "So it would be imprudent at this point to take too much reassurance" from the small number of deaths.
"We have seen times where things appear to be getting better and then get worse again," said Dr. Anne Schuchat, the U.S. agency's interim science and public health deputy director. "I think in Mexico we may be holding our breath for some time."
The global caseload was nearing 800 and growing _ the vast majority in Mexico, the U.S. and Canada. Costa Rica reported its first confirmed swine flu case _ the first in Latin America outside Mexico.
Swine flu cases have been confirmed in 18 countries so far _ including Europe, the Middle East and the Asia-Pacific region _ and experts believe the actual spread is much wider than the numbers suggest.
U.S. President Barack Obama urged caution Saturday.
"This is a new strain of the flu virus, and because we haven't developed an immunity to it, it has more potential to cause us harm," Obama said. Later, he spoke with Mexican President Felipe Calderon for about 20 minutes to share information.
What started as a swine flu outbreak more than a week ago in Mexico quickly ballooned to a global health threat, with the WHO declaring a pandemic was imminent. Now public health officials are having to carefully calibrate their statements. Push the message too far, and they could lose credibility if the virus fizzles out. But if they back off and it suddenly surges, the consequences could be much more dire.
Some Mexicans have criticized their government for reacting too slowly to the outbreak at first, and now for overreacting in ordering a five-day, nationwide shutdown of all nonessential government and private business. Responding to the attacks, Health Secretary Jose Angel Cordova said: "It's absurd to think that Mexico was putting on a show. I think it's preferable, at a certain moment, to take advanced measures and succeed in containing the problem than to not take them and ask, 'Why didn't we take them?'"
However, Cordova said hospitals are now handling fewer patients with swine flu symptoms, a sign that the disease is presently not very contagious. Mexican investigators who visited 280 relatives of victims found only four had the virus.
But experts said there is much they don't know about the outbreak in Mexico. A multinational team of virus sleuths are trying to piece together the epidemiological puzzle.
Cordova said 12 of the dead were between 21 and 40 _ unusual ages for people to die of the flu because they tend to have stronger immune systems.
Three of the dead were children: a 9-year-old girl, a 12-year-old girl and a 13-year-old boy, said Pablo Kuri, an epidemiologist and adviser to Cordova. Four were older than 60.
Although most of the dead were from Mexico City, they came from different neighborhoods in the metropolis of 20 million people, Kuri said. One common factor may be that they sought treatment too late _ an average of seven days before seeing a doctor. For those who recovered, the average wait was three days, said Hugo Lopez-Gatell Ramirez, deputy director of Mexico's Intelligence Unit for Health Emergencies.
Many of the sick around the world were people who had visited Mexico, including 13 of Britain's 15 cases.
South Korea reported Asia's second confirmed case _ a woman just back from Mexico _ and other governments prepared to quarantine airline passengers, eager to show how they have learned from the deadly SARS epidemic in 2003, when Hong Kong was criticized for imposing quarantines too slowly.
China suspended all direct flights from Mexico and sealed 305 people inside a Hong Kong hotel where an infected Mexican tourist stayed. Health workers in white bodysuits patrolled the lobby where the 25-year-old Mexican stayed before he became Asia's first confirmed case late Friday.
Mexican Foreign Minister Patricia Espinosa complained that China had isolated several Mexicans without reason _ and urged Mexicans not to travel to China until the situation was resolved.
"These are discriminatory measures," she said.
Associated Press writers David B. Caruso in New York and Juan Carlos Llorca in Mexico City contributed to this report.