The United States launched border screening for swine flu exposure on Monday morning amid concern for a possible global pandemic while President Barack Obama said there was no immediate cause for alarm.

Richard Besser, acting director of the US Centers for Disease Control, revealed that the US authorities were starting to undertake "passive screening" at its borders. He restated the Obama administration's call on Sunday for people to stay calm.

He reported that US border officials would be "asking people about fever and illness, looking for people who are ill."

Besser traveled the morning news-show circuit Monday, telling interviewers the US government was being "extremely aggressive" and he wouldn't personally recommend traveling to parts of Mexico where the new virus has taken hold.

He noted that the issue of a travel ban was under discussion, but nothing had been decided.

However, Besser warned the public Monday to brace for more swine flu cases and possibly even death from the killer disease, which already has claimed more than 100 lives in neighboring Mexico.

In remarks delivered at a gathering of the National Academy of Sciences, Obama said that the ailment, which has killed more than 100 people in Mexico, "requires a heightened state of alert. But it is not a cause for alarm."

"The Department of Health and Human Services has 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," the president said.

Responding to what some health officials feared could be the leading edge of a global pandemic emerging from Mexico, American health officials declared a public health emergency on Sunday as 20 cases of swine flu were confirmed in this country, including eight in New York City.

Other nations imposed travel bans or made plans to quarantine air travelers as confirmed cases also appeared in Mexico and Canada and suspect cases emerged elsewhere.

The emergency declaration in the United States lets the government free more money for anti-viral drugs and give some previously unapproved tests and drugs to children. It will also allowed Washington to ship roughly 12 million doses of flu-fighting medications from a federal stockpile to states in case they eventually need them.

Besser said besides the eight New York cases, seven had been confirmed in California, two in Kansas, two in Texas and one in Ohio. The virus looked identical to the one in Mexico believed to have killed 103 people and sickened about 1,600. As of Sunday night, there were no swine flu deaths in the United States, and one hospitalization.

The A/H1N1 swine flu confirmed in the Mexican, US and Canadian cases is a previously unknown combination of pig, human and avian flu viruses. Pigs, which are easily infected with all three types of flu, can function as "mixing vessels" in which flu viruses exchange genetic material and emerge in new forms.

(Xinhua News Agency April 28, 2009)