A man with underlying heart conditions became the third person infected with swine flu to die in the United States and Costa Rica reported the disease's first fatality outside North America, health authorities said.
Japanese authorities, meanwhile, scrambled to limit contact with their country's first cases, and Australia and Norway joined the list of nations with confirmed cases of swine flu.
In Washington state, a Snohomish County man in his 30s died on Thursday from what appeared to be complications from swine flu, the state Department of Health said in a statement issued Saturday. The man had underlying heart conditions and viral pneumonia at the time of his death, but swine flu was considered a factor in his death, the statement said.
The man, who was not identified, reportedly began showing symptoms on April 30.
His death and the death of a 53-year-old man in Costa Rica on Saturday brings the global death toll to 53, including 48 in Mexico, three in the United States and one in Canada.
Like other deaths outside Mexico, the Costa Rican man suffered from complicating illnesses, including diabetes and chronic lung disease, the Health Ministry said.
Previously, U.S. authorities reported swine flu deaths of a toddler with a heart defect and a woman with rheumatoid arthritis, and Canadian officials said the woman who died there also had other health problems but gave no details.
In Mexico, where 48 people with swine flu have died, most of the victims have been adults aged 20 to 49, and many had no reported complicating factors. People with chronic illnesses usually are at greatest risk for severe problems from flu, along with the elderly and young children.
The Costa Rican fatality was one of eight swine flu cases in the country confirmed by the U.S. Centers for Disease Control and Prevention, Health Minister Maria Luisa Avila told The Associated Press.
Avila said officials had been unable to determine how the Costa Rican patients became infected, but she said the man who died had not recently traveled abroad. Many flu sufferers in other nations have been linked to recent trips to the United States or Mexico.
Mexico, which raised its count of confirmed cases to 1,626 based on tests of earlier patients, continued to gradually lift a nationwide shutdown of schools, businesses, churches and soccer stadiums.
But an upswing in suspected — though not confirmed — cases in parts of Mexico prompted authorities in at least six of the country's 31 states to delay plans to let primary school students return to class on Monday after a two-week break.
"It has been very stable ... except for those states," Health Department spokesman Carlos Olmos said, referring to states in central and southern Mexico.
Mexican health authorities released a breakdown of the first 45 of the country's 48 flu deaths that showed that 84 percent of the victims were between the ages of 20 and 54. Only 2.2 percent were immune-depressed, and none had a previous history of respiratory disease.
In Japan, authorities quarantined a high school teacher and three teenage students who tested positive in an airport test for swine flu after they returned from a school trip to Canada. Officials said they were working with the World Health Organization to contact at least 13 people on the flight who had gone on to other destinations.
Japanese Health and Welfare Minister Yoichi Masuzoe acknowledged it would be difficult to trace everyone who came into contact with the infected Japanese, who visited Ontario on a home-stay program in a group of about 30 students. The three were isolated and recovering at a hospital near Narita International Airport.
"There are limitations to what we can do, but we will continue to monitor the situation and strengthen or relax such measures as needed," he told reporters.
Public broadcaster NHK TV urged people who were aboard the same Northwest Airlines flight from Detroit to call a special telephone number for consultations. So far, 49 people had been traced and would be monitored for 10 days, officials said.
Australia reported its first case Saturday in a woman it said was no longer infectious. She first noticed her symptoms while traveling in the U.S., federal Health Minister Nicola Roxon told reporters.
New Zealand — the first country in the Asia-Pacific region to confirm cases — reported two more Saturday for a total of seven. The two high school students returned last month from a school trip to Mexico. Six of the country's cases were in students and a teacher on that trip; the seventh traveled on the same plane as the group.
Norway's National Health Directorate reported that country's first two confirmed cases: a man and a woman, both aged 20, who had been studying in Mexico.
In Canada, officials said almost 500 hogs quarantined on an Alberta farm after being diagnosed with swine flu had been killed because animals were becoming overcrowded since the facility was barred from shipping any to market.
"They were not culled for being sick. They were culled because of animal welfare concerns," Dr. Gerald Hauer, the province's chief veterinarian, told reporters. He said about 1,700 pigs remained on the farm.
Authorities have said the pigs apparently became infected from a farm worker who had been in Mexico. Experts say people cannot catch flu from eating pork, but in rare cases people have been infected by contact with a live pig.