MEXICO CITY — The swine flu epidemic crossed new borders Tuesday with the first cases confirmed in the Middle East and the Asia-Pacific region, as world health officials said they suspect American patients may have transmitted the virus to others in the U.S.
Most people confirmed with the new swine flu were infected in Mexico, where the number of deaths blamed on the virus has surpassed 150.
But confirmation that people have been infecting others in locations outside Mexico would indicate that the disease was spreading beyond travelers returning from Mexico, World Health Organization spokesman Gregory Hartl told reporters on Tuesday in Geneva.
Hartl said the source of some infections in the United States, Canada and Britain was unclear.
Hartl said WHO was waiting for U.S. authorities to announce that a number of students at a New York high school have passed the virus on to one another after their return from a spring vacation in Mexico. "I think we might have one other instance in the U.S.," he said.
Pressed by reporters to elaborate, he declined, saying it was up to U.S. authorities to provide further information.
Possible scenarios include students getting infected who did not travel to Mexico, or students who traveled there but became infected only after returning to the United States, or family members getting infected by returning students.
WHO calls this "community transmission" and says it's a key test for gauging whether the spread of the virus has reached pandemic proportions. The swine flu has already spread to at least six countries besides Mexico, which prompted WHO officials to raise its alert level on Monday.
"At this time, containment is not a feasible option," said Keiji Fukuda, assistant director-general of the World Health Organization.
New Zealand reported Tuesday that 11 people who recently returned from Mexico contracted the virus. Tests conducted at a WHO laboratory in Australia had confirmed three cases of swine flu among 11 members of the group who were showing symptoms, New Zealand Health Minister Tony Ryall said.
Officials decided that was evidence enough to assume the whole group was infected, he said.
Israel's Health Ministry confirmed Tuesday the region's first swine flu case in the city of Netanya. The patient, 26, recently returned from Mexico and had contracted it. A hospital official said the patient had recovered, but will remain hospitalized until the health ministry approves his release.
Another suspected case has been tested at another Israeli hospital but results are not in, the ministry said.
Meanwhile, a second case was confirmed Tuesday in Spain, Health Minister Trinidad Jimenez said, a day after the country reported its first case. The 23-year-old student, one of 26 patients under observation, was not in serious condition, Jimenez said.
With the virus spreading, the U.S. prepared for the worst as President Barack Obama tried to reassure Americans. Obama said the outbreak is "not a cause for alarm," even as the U.S. stepped up checks of people entering the country and warned U.S. citizens to avoid nonessential travel to Mexico.
"We anticipate that there will be confirmed cases in more states as we go through the coming days," Homeland Security Secretary Janet Napolitano said on NBC's "Today" show on Tuesday.
The Food and Drug Administration late Monday issued emergency guidance that allows certain antiviral drugs to be used in a broader range of the population in case mass dosing is needed to deal with a widespread swine flu outbreak.
The European Union health commissioner suggested that Europeans avoid nonessential travel both to Mexico and parts of the United States. Russia, Hong Kong and Taiwan said they would quarantine visitors showing symptoms of the virus.
Mexico, where the number of deaths believed caused by swine flu rose by 50 percent on Monday to 152, is suspected to be ground zero of the outbreak. But Mexican Health Secretary Jose Angel Cordova late Monday said no one knows where the outbreak began, and implied it may have started in the U.S.
"I think it is very risky to say, or want to say, what the point of origin or dissemination of it is, given that there had already been cases reported in southern California and Texas," Cordova said in a news conference.
Dr. Nancy Cox of the Atlanta-based Centers for Disease Control and Prevention has said she believes the earliest onset of swine flu in the U.S. was on March 28. Cordova said a sample taken from a 4-year-old boy in Mexico's Veracruz state in early April tested positive for swine flu. However, it is not known when the boy, who later recovered, became infected.
WHO raised the alert level to Phase 4, meaning there is sustained human-to-human transmission of the virus causing outbreaks in at least one country. Monday was the first time it has ever been raised above Phase 3.
Putting an alert at Phases 4 or 5 signals that the virus is becoming increasingly adept at spreading among humans. Phase 6 is for a full-blown pandemic, characterized by outbreaks in at least two regions of the world.
Fifty cases — none fatal and most of them mild — were confirmed in the United States. Including the New Zealand, Israeli and new Spanish reports, there were 92 confirmed cases worldwide on Tuesday. That included six in Canada, one in Spain and two in Scotland.
Amid the alarm, there was a spot of good news. The number of new cases reported by Mexico's largest government hospitals has been declining the past three days, Cordova said, from 141 on Saturday to 119 on Sunday and 110 Monday.
Symptoms of the swine flu include a fever of more than 100, coughing, joint aches, severe headache and, in some cases, vomiting and diarrhea. Many victims have been in their 30s and 40s — not the very old or young who typically succumb to the flu.
So far, no deaths from the new virus have been reported outside Mexico.
It could take four to six months before the first batch of vaccines are available, WHO said. Some anti-flu drugs do work once someone is sick.
The best way to keep the disease from spreading, the CDC's acting director, Richard Besser, said, is by taking everyday precautions such as frequent handwashing, covering up coughs and sneezes, and staying away from work or school if not feeling well.
Flu deaths are nothing new in the United States. The CDC estimates that about 36,000 people died of flu-related causes each year, on average, during the 1990s in the United States. But the new flu strain is a combination of pig, bird and human viruses against which humans may have no natural immunity.
AP writers Mark Stevenson in Mexico City, Mike Stobbe in Atlanta, Ray Lilley in Wellington, New Zealand, Aron Heller in Jerusalem and Pan Pylas in London contributed to this report.