April 25 (Bloomberg) -- The World Health Organization is set to declare the deadly swine flu virus outbreak in Mexico and the U.S. a global concern, potentially prompting travel advisories, said a person familiar with the matter.

An emergency committee of the WHO in Geneva will declare the outbreak “a public health event of international concern” in a teleconference that began at 4 p.m. today, said the person, who spoke on condition of anonymity because the meeting is confidential. In response, WHO Director-General Margaret Chan may raise the level of pandemic alert, which could lead to travel advisories aimed at curbing the disease’s spread.

Human-to-human spread of the previously unknown H1N1 swine influenza in Mexico and the U.S. is heightening concern that the virus may spark a pandemic. At least 68 people have died and more than 1,000 have fallen ill with flu-like symptoms around Mexico City in the past month, officials said. The outbreak has pandemic potential, Chan said.

“The situation is evolving quickly,” she said on a conference call with reporters today. “A new disease is by definition poorly understood. We do not yet have a complete picture of the epidemiology or the risk, including the possible spread. In the assessment of the WHO, this is a serious situation which must be watched very closely.”

The emergency committee will consider whether to declare the outbreak a matter of international concern, and whether to recommend travel advisories, Chan told journalists before the panel’s meeting.

Closing Theaters

There’s no sign the outbreak has spread beyond Mexico and the U.S., she said. Three main human flu strains -- H3N2, H1N1 and type-B -- circulate and cause 250,000 to 500,000 deaths a year in seasonal epidemics, according to the WHO. Pandemics occur when a novel influenza A-type virus, to which almost no one has natural immunity, emerges and begins spreading.

Mexico’s Social Security Institute shut all of the theaters and cultural centers it operates nationwide to avoid spreading the flu strain -- reminiscent of actions implemented during the 2003 SARS outbreak in Asia. Travel curbs imposed there damaged economies throughout the region, where that virus circulated most widely.

In Singapore, where 33 infected people died, gross domestic product shrank 11.4 percent in the second quarter of 2003 because of the severe acute respiratory syndrome.

Pandemic Threat

Swine flu was confirmed in 20 of the deaths so far in Mexico. Of 14 tissue samples tested from Mexico, half were a genetic match with the swine flu reported in eight people in California and Texas, the Atlanta-based Centers of Disease Control and Prevention said.

“We do not know whether this swine flu virus or some other influenza virus will lead to the next pandemic,” Richard Besser, the CDC’s acting director, told reporters yesterday on a teleconference. “Scientists around the world continue to monitor the virus and take its threat seriously.”

The new influenza strain, a conglomeration of genes from swine, bird and human viruses, poses the biggest threat of a large-scale flu pandemic since the emergence of the H5N1 strain that has killed millions of birds and hundreds of people, said William Schaffner, an influenza expert at Vanderbilt University School of Medicine in Nashville, Tennessee.

“It re-combined to create something totally new,” David Butler-Jones, Canada’s chief public health minister, told reporters yesterday. “How, when, or where it did that I don’t think we know. What it will lead to is impossible to predict.”

Alert System

WHO’s alert level is at level 3, meaning there is no, or very limited, human-to-human transmission of a potential pandemic virus. Officials at the agency have said the global spread of the H5N1 bird flu virus since 2003 has put the world closer to another influenza pandemic than at any time since 1968, when the last of the previous century’s three pandemics occurred.

WHO uses a six-step alert system to tell the world what preparations to take in response to a pandemic. Flu can spread quickly when a new strain emerges because no one has natural immunity and a vaccine takes months to develop. The 1918 Spanish Flu pandemic, which killed as many as 50 million people, began when an avian flu virus jumped to people, doctors said.

“These levels of pandemic alert are all signals for action,” said Malik Peiris, a professor of microbiology at the University of Hong Kong, who has studied influenza viruses for more than a decade. “Raising the level of alertness to influenza, especially in returning travelers, would be a relevant thing to do.”

Tracing the Spread

It’s premature to draw parallels between the current outbreak and the 1918 flu, Chan said.

Teams of disease investigators have been sent to California and Texas to trace how the malady has spread, and the U.S. offered to send scientists to Mexico, said the CDC’s Besser. U.S. hospitals are being asked to collect samples from patients with flu-like symptoms, said Schaffner, chief of preventive medicine at Vanderbilt, in a telephone interview yesterday.

“They are asking us who work in hospitals to go to our emergency rooms and our pediatric wards to gather specimens and start testing them,” Schaffner said. “This has a sense of urgency about it.”

Mexico’s government has closed schools, museums, movie theaters and libraries in Mexico City and surrounding areas until further notice, according to an e-mail from the National Arts and Culture Council. It’s also handing out free facemasks and extending the deadline for filing taxes until May 31, Jose Cordova, Mexico’s Health Minister, told reporters yesterday. A million doses of antiviral medicine are available for distribution, he said.

Twenty-four cases, including three deaths, have been reported in San Luis Potosi, in central Mexico, and four cases have been found in Mexicali near the border with the U.S., according to the WHO.

To contact the reporter on this story: Jason Gale in Singapore at j.gale@bloomberg.net

Last Updated: April 25, 2009 10:57 EDT