As more details emerged Monday on the origins of the swine flu outbreak, the World Health Organization raised its infectious disease alert level for the first time ever, and U.S. authorities warned against unnecessary travel to Mexico.
In that country, authorities ordered all schools closed nationwide, and officials disclosed that the outbreak began much earlier than thought, near a pig farm in the Veracruz municipality of Perote.
And, it was revealed, the first confirmed fatality worked as a door-to-door census-taker in one of Mexico's poorest states.
Mexican health authorities said that they are doing everything possible to track the outbreak, but that they don't have enough personnel even to visit the houses of those who died. Aid is coming in from around the world, both in workers to help with the epidemiology and in funds to help provide antiviral drugs and other materials.
The U.S. government still considers the situation an outbreak but is responding as if it were a pandemic, said Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention. The agency is distributing antiviral drugs -- a quarter of its total stockpile -- to state authorities, increasing surveillance at borders and providing test kits to help identify the virus.
Even so, he struck a note of caution, saying that the rise in cases doesn't mean swine flu is spreading, only that more testing is being completed. Because of this, numbers will continue to rise. WHO officials said they would become alarmed only if large outbreaks occur in isolated communities through confirmed transmission from the original victims. That would mean that it is spreading easily.
Other countries responded with more obvious alarm. Malaysia, Singapore, Japan and other Asian nations monitored airline passengers from North America for fever or other signs of illness. Russia and China banned pork from Mexico and three U.S. states, even though the virus can't be contracted by eating pork. And the European Union's health minister suggested that nonessential travel to the U.S. be avoided.
Though the actions were termed an abundance of caution, airline and travel industries took a hit, fears grew that the U.S. economy could face further threats, and nations around the world tested sniffling citizens and sent out alarmed reports about possible flu cases.
In Mexico, authorities said Monday that 149 people have died of influenza, and at least 1,995 cases have been reported at hospitals. So far, however, only 26 of the deaths and 172 of the cases have been confirmed to be swine flu.
As of Monday night, 26 new cases of swine flu had been confirmed in the United States -- 20 in New York, five in California and one in Texas.
Although the cases had more than doubled since Sunday, all the new cases were mild. There have been only two hospitalizations in this country, both in California.
Gregory Hartl, a spokesman for the WHO, said that one swine flu case had been confirmed in Albacete, Spain, marking the first time the virus had been seen in Europe. British health authorities later said that two cases had been confirmed in Scotland. All were among travelers who had recently returned from Mexico.
All three cases were described as mild, although the patients have been hospitalized for quarantine, which officials called standard procedure. Hartl said there have been "rumors of cases in other countries," but as of Monday evening none had been confirmed to be swine flu.
In California, Sacramento County Public Health Officer Dr. Glenna Trochet said that swine flu had been confirmed in three students at St. Mel's Catholic School in Fair Oaks. All had mild cases and recovered or are recovering.
Dr. Gil Chavez of the California Department of Public Health said 13 cases had been confirmed in the state: five in San Diego County, five in Imperial County and three in Sacramento County. He said there were two more "probable" cases in San Diego County.
Chavez said that beginning today, California will become the first state with the capability to test samples for swine flu. Until now, all suspected samples had to be sent to the CDC for analysis.
Speaking at an impromptu news conference Monday in Beverly Hills, Gov. Arnold Schwarzenegger said: "I can assure you that at this time there is no reason for alarm, but we want to go and do everything that we can to make sure that we prevent an outbreak here."
A New York City health official said the 20 new cases there were among students and teachers at St. Francis Preparatory School in Queens, where eight cases were previously observed. He said there also were 17 "probable" cases among the group and noted that the new cases were due to continuation of the testing program.
Mayor Michael Bloomberg said the number of cases at the private high school could climb as high as 100.
Texas authorities said a third case had been confirmed in Guadalupe County, bringing the total in that state to three.