WASHINGTON (AP) _ U.S. officials advised Americans against most travel to Mexico on Monday as a swine flu virus that began there spread to the United States and beyond. With more than 40 cases now reported in the U.S., President Barack Obama urged calm, saying there 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 disease in the United States seems less severe than the outbreak in Mexico, where more than 1,600 cases have been reported and where the suspected death toll has climbed to 149. No deaths have been reported in the U.S, and only one hospitalization.

“I wouldn’t be overly reassured by that,” Besser told reporters at CDC’s headquarters in Atlanta. He raised the possibility of more severe cases _ and deaths _ in the United States.

Authorities on Tuesday were investigating a possible case of swine flu at Disney World near Orlando.

A European Union official warned against travel to parts of the U.S. as well as Mexico, but Besser said that seemed unwarranted.

State Department spokesman Robert A. Wood said the EU commissioner’s remarks were his “personal opinion,” not an official position, and thus the department had no comment. “We don’t want people to panic at this point,” Wood said.

Still Besser said of the situation, “We are taking it seriously and acting aggressively. … Until the outbreak has progressed, you really don’t know what it’s going to do.”

The U.S. stepped up checks of people entering the country by air, land and sea. The CDC can send someone to the hospital if they suspect a case, but no one was being refused entry.

A new U.S. travel advisory was being prepared suggesting “nonessential travel to Mexico be avoided,” Besser said.

The confirmed cases announced on Monday were more than double the 20 earlier reported by the CDC. Besser said this was due to further testing _ not further spreading of the virus _ at a school in New York City. Besser said other cases have been reported in Ohio, Kansas, Texas and California. A few schools in the affected areas have closed as a precaution.

U.S. authorities are not currently recommending that people put on masks in the workplace to protect against infection. The evidence “is not that strong” that the wearing of protective masks effectively limits the outbreak of such diseases, Besser said.

While there presently is no vaccine available to prevent the specific strain now being seen, there are antiflu drugs that do work once someone is sick.

Besser said about 11 million doses of flu-fighting medications from a federal stockpile have been sent to states in case they are needed _ roughly one quarter of the doses in the stockpile.

The best way to keep the disease from spreading is by everyday precautions such as frequent hand washing, covering up coughs and sneezes and staying away from work or school if not feeling well, Besser said.

While the cases reported so far in the United States seem relatively mild, Besser said far more will be known about the disease’s transmission traits and severity in a week or two. He said the particular virus at issue had not been seen before, either in the United States nor in Mexico.

Countries across the globe increased their vigilance amid increasing worries about a worldwide pandemic. Obama, who appointed Besser as interim head of the CDC in January, told a gathering of scientists that his administration’s Department of Health and Human Services had declared a public health emergency “as a precautionary tool to ensure that we have the resources we need at our disposal to respond quickly and effectively.”

“This is obviously a cause for concern and requires a heightened state of alert, but it’s not a cause for alarm,” Obama said. He said he was getting regular updates.

Obama went to Mexico earlier this month, but the White House said Monday the president has shown no symptoms of swine flu and that his health was never in danger.

The Senate has yet to confirm a secretary of human services, a surgeon general or a director of CDC. The absence of those officials left Besser and Homeland Security Secretary Janet Napolitano to brief reporters on the swine flu outbreak.

Napolitano told reporters at a news conference Monday that travel warnings to Mexico will remain in place as long as swine flu is detected.

U.S. customs officials began checking people entering U.S. territory. Officers at airports, seaports and border crossings were watching for signs of illness, said Customs and Border Protection spokesman Lloyd Easterling.

While “the borders are open,” Easterling said officials were “taking a second look at folks who may be displaying a symptom of illness.”

If a traveler reports not feeling well, the person will be questioned about symptoms and, if necessary, referred to a CDC official for additional screening, Easterling said. The customs officials were wearing personal protective gear, such as gloves and masks, he said.

Several airlines said they were waiving usual penalties for changing reservations for anyone traveling to, from, or through Mexico, but had not canceled flights.


Associated Press writers Mark Stevenson and Olga R. Rodriguez in Mexico City; Frank Jordans in Geneva; Mike Stobbe in Atlanta; Maria Cheng in London and Eileen Sullivan and Robert Burns in Washington contributed to this report.

Pictured above is Dr. Richard Besser, acting director of the U.S. Centers for Disease Control and Prevention.