MEXICO CITY — The swine-flu epidemic entered a dangerous new phase Monday as the death toll climbed in Mexico and the number of suspected cases there and in the United States nearly doubled.
The World Health Organization raised its alert level but stopped short of declaring a global emergency.
The United States advised Americans against most travel to Mexico and ordered stepped-up border checks in neighboring states.
The European Union health commissioner advised Europeans to avoid nonessential travel to Mexico and parts of the U.S.
The suspected number of deaths rose to 149 in Mexico, the epicenter of the outbreak with nearly 2,000 people believed to be infected.
The number of U.S. cases rose to 40, the result of further testing at a New York City school, although none was fatal. Other U.S. cases have been reported in Ohio, Kansas, Texas and California.
Mexican Health Secretary Jose Angel Cordova said the epidemic was entering an extremely dangerous phase, with the number of people infected mushrooming even as authorities desperately ramped up defenses.
“We are in the most critical moment of the epidemic. The number of cases will keep rising, so we have to reinforce preventative measures,” Cordova said at a news conference.
The WHO raised its alert level to Phase 4, meaning there is sustained human-to-human transmission of the virus causing outbreaks in at least one country.
Its alert system was revised after bird flu in Asia began to spread in 2004, and Monday was the first time it was raised above Phase 3.
“At this time, containment is not a feasible option,” as the virus has already spread to several countries other than Mexico, said WHO Assistant Director-General Keiji Fukuda.
Putting an alert at Phase 4 or 5 signals that the virus is becoming increasingly adept at spreading among humans. That move could lead governments to set trade, travel and other restrictions aimed at limiting its spread.
Phase 6 is for a full-blown pandemic, characterized by outbreaks in at least two regions of the world.
It could take four to six months before the first batch of vaccines is available to fight the virus, WHO officials said.
Russia, Hong Kong and Taiwan said they would quarantine visitors showing symptoms of the virus amid global fears of a pandemic.
President Barack Obama said the outbreak was reason for concern but not yet “a cause for alarm.” Dr. Richard Besser, acting director of the Centers for Disease Control and Prevention, said that so far the virus in the United States seems less severe than in Mexico. Only one person in the U.S. has been hospitalized.
“I wouldn’t be overly reassured by that,” Besser told reporters at CDC headquarters in Atlanta, raising the possibility of more severe cases in the U.S.
“We are taking it seriously and acting aggressively,” Besser said. “Until the outbreak has progressed, you really don’t know what it’s going to do.”
U.S. customs officials began checking people entering U.S. territory. Millions of doses of flu-fighting medications from a federal stockpile were on their way to states, with priority given to the five already affected and to border states. Federal agencies were conferring with state and international governments.
“We want to make sure that we have equipment where it needs to be, people where they need to be and, most important, information shared at all levels,” said Janet Napolitano, head of the Homeland Security Department. “We are proceeding as if we are preparatory to a full pandemic.”
She said travel warnings for trips to Mexico would remain in place as long as swine flu is detected.
Mexico canceled school at all levels nationwide until May 6, and the Mexico City government said it was considering a complete shutdown, including all public transportation, if the death toll keeps rising. Labor Secretary Javier Lozano Alarcon said employers should isolate anyone showing up for work with a fever, cough, sore throat or other signs of the flu.
Amid the warnings, the Mexican government grappled with increasing criticism of its response. At least two weeks after the first swine-flu case, the government has yet to say where and how the outbreak began or give details on the victims.
The health department lacked the staff to visit the homes of all those suspected to have died from the disease, Cordova said.
Cordova said 1,995 people have been hospitalized with serious cases of pneumonia since the first case of swine flu was reported April 13. The government does not yet know how many were swine flu.
He said tests show a 4-year-old boy contracted the virus before April 2 in Veracruz state, where a community has been protesting pollution from a large pig farm.
The farm is run by Granjas Carroll de Mexico, a joint venture half owned by Virginia-based Smithfield Foods, Inc. Spokeswoman Keira Ullrich said the company has found no clinical signs or symptoms of the presence of swine flu in its herd or its employees working anywhere in Mexico.
WHO spokesman Peter Cordingley singled out air travel as an easy way the virus could spread, noting that the WHO estimates that up to 500,000 people are on planes at any time.
