April 27 (Bloomberg) -- Fears of globally spreading swine flu cases spurred the World Health Organization to raise its pandemic alert to an unprecedented level as the U.S. confirmed 40 cases and Mexico’s death toll reached 149.

The Geneva-based health agency raised its six-stage pandemic alert level to 4 from 3 because of evidence of increased human-to-human contact, said Keiji Fukuda, the WHO’s assistant director-general for health security and environment. U.S. officials are urging that nonessential travel to Mexico be avoided, the European Union has told travelers to avoid outbreak areas, and Australia, Japan, Singapore and South Korea are screening air passengers.

Whether the outbreak becomes a lethal pandemic lies in the nature of flu germs, which mutate readily and can become virulent by exchanging genes with related viruses. While the H5N1 bird virus that spread across Asia never gained genes to spread easily among humans, the Mexican swine flu already has, said Malik Peiris, a researcher at the University of Hong Kong.

“The surveillance system has been cranked up to a very sensitive level and what we’re getting, and what we expect a lot more of, are rumors of cases and these cases will be investigated,” said Dick Thompson, a spokesman for the World Health Organization in Geneva. “There will be rapid clinical laboratory testing to see whether or not these sick people are indeed sick with swine flu.”

Pandemics occur when a novel influenza A-type virus, to which almost no one has natural immunity, emerges and spreads internationally.

U.S. Response

President Barack Obama’s administration declared a public health emergency due to the U.S. outbreak.

While the U.S. cases have been mild and no one died, health authorities “fully expect we will see a broader range” of severity, said Richard Besser, acting chief of the U.S. Centers for Disease Control and Prevention in a call with reporters.

“We don’t think that any of the existing vaccines are effective,” Besser said today. “There are discussions ongoing about whether to make a vaccine and whether that should be undertaken. It’s not an easy decision.”

Swine flu is a respiratory disease of pigs caused by type-A influenza that regularly leads to outbreaks among the animals, according to the Atlanta-based CDC. 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.

Heightened Concern

Obama said today the emergence and spread of swine flu in the U.S. merits heightened concern “but it’s not a cause for alarm.” The 40 confirmed U.S. cases doubled from yesterday and were found in California, Kansas, New York, Ohio and Texas, according to the CDC.

New York City has 28 confirmed cases of swine flu, all from St. Francis Preparatory School in Queens, Mayor Michael Bloomberg said today at a news conference. All the cases were mild and as many as 100 may ultimately be found at the school, the mayor said.

The U.S. Department of Health and Human Services issued an emergency declaration as a “precautionary tool” to free resources to monitor and respond to the spread of the virus, Obama said today in a speech to the National Academy of Sciences in Washington.

WHO declared the outbreak a “public health emergency of international concern” on April 25. The number of confirmed cases in Mexico is 26, said WHO spokesman Gregory Hartl today on a conference call. Mexico Health Minister Jose Cordova said 149 people may have died in Mexico from an outbreak of swine flu, though the cause of the deaths hasn’t been confirmed.

Politics, Not Policy

Internationally, Australia, Japan, Singapore and South Korea have said they are screening travelers for fever, while Hong Kong raised its swine-flu response level to “serious” from “alert.” Brazil said it was warning passengers traveling to the U.S., Mexico and Canada about the flu. Spain also reported its first case of swine influenza

Travel restrictions are unnecessary and based on political, not medical considerations, said Margaret Chan, World Health Organization chief.

“We know from past experience that transmission of influenza or the spread of new influenza disease would not be stopped by closing borders and would not be stopped by restricting movement of people or goods,” Chan, director- general, of the United Nations agency, said today in a conference call with international health group leaders.

Global Spread

Six people in Canada contracted swine flu and more cases are likely, government officials said. New Zealand officials said as many as 13 students who recently visited Mexico may have swine flu.

One person in Spain has been confirmed as suffering from swine flu in Europe’s first case of the disease, Health Minister Trinidad Jimenez said. A further 16 people are being tested for the flu, she said. The confirmed case and possible infections involve people who had been in Mexico, where swine flu first broke out.

Ten high-school students who returned to New Zealand on April 25 from Mexico tested positive for influenza A, Health Minister Tony Ryall said in Wellington. Three students from another school are ill and being tested for the flu, he said.

Bars, Movie Theaters, Churches

The Mexican government requested that bars, movie theaters and churches be closed in Mexico City. It also extended its school closure to May 6 and may shut down more activities, Cordova said.

Mexico City Mayor Marcelo Ebrard said the city has a shortage of face masks that health authorities say may help slow the spread of flu. The city will pass out 1 million more masks today and another 4 million tomorrow, Ebrard said in an interview on Radio Formula.

In New York, authorities are keeping city schools open and urging residents to wash their hands frequently, stay home if ill and avoid the hospital unless very sick.

EU officials “strongly recommend avoiding” travel to Mexico and other areas affected by the virus, EU Health Commissioner Androula Vassilou said in a videotaped statement released in Brussels today. The EU won’t advise against traveling to Spain.

Airline Stocks Fall

Airline stocks tumbled worldwide, dragging a benchmark U.S. index to its biggest drop in two months, on fears the swine flu outbreak will damp travel demand. The Bloomberg U.S. Airlines Index fell 11 percent, the most since Feb. 20, while the Bloomberg World Airlines Index fell 7.5 percent.

U.S. stocks retreated overall with concerns about the flu affecting travel, energy and hotel companies. The Standard & Poor’s 500 Index fell 1 percent to 857.5, the Dow Jones Industrial Average declined 51.29 points, or 0.6 percent, to 8,025.

WHO declared the outbreak a “public health emergency of international concern” on April 25. Swine flu results in symptoms similar to regular human influenza such as fever, lethargy and cough, and may also cause nausea, vomiting and diarrhea, according to the CDC.

“We don’t know what’s going to happen going forward because it’s certainly possible this virus could change in terms of its patterns of transmissions or virulence,” said Frederick G. Hayden, a professor of clinical virology at the University of Virginia School of Medicine in Charlottesville, Virginia.

Seeking Answers

Disease trackers are looking for sustained, human-to-human transmission of the viruses in the community to determine whether the WHO needs to elevate its level of pandemic alert.

Swine-flu viruses aren’t transmitted by food, and eating properly handled and cooked pork and pork products is safe, according to the CDC. There’s no evidence the disease is spread by exposure to “pork or pigs,” said the WHO’s Fukuda said.

Scientists are trying to determine why the virus has been more severe in Mexico. In the U.S. only one person has required hospitalization, said Besser of the CDC.

Homeland Security Secretary Janet Napolitano said 25 percent of “courses of treatments” of drugs, known as antivirals, were being released from U.S. stockpiles. In all, there are 50 million courses, she said. Among those are Tamiflu, sold by Roche Holding AG, and Relenza, from GlaxoSmithKline.

Quick Identification

John Brennan, a special assistant to Obama for homeland security, said the government is putting in place systems to allow “rapid identification” of any new cases and efforts to “mitigate a broader outbreak” in the U.S.

Every day, more than 1 million people -- U.S. citizens and foreigners -- seek entry into one of the U.S.’s 325 ports of entry, according to the Department of Homeland Security. About 20 percent of those entering the U.S. come by air and around 74 percent by land.

Canada also is considering advisories for those traveling to and from Mexico, Canadian Health Minister Leona Aglukkaq said today.

Singapore tightened checks at Changi airport to screen arriving passengers, the Health Ministry said. Malaysia placed officials at airports to screen travelers, and told hospitals and clinics to check for patients with unusual fevers.

Japan will heighten its monitoring for any signs of swine flu and authorities will examine flights from Mexico, Chief Cabinet Secretary Takeo Kawamura said today.

Border Checks

Taiwan has tightened border checks for visitors from Mexico and the U.S., while Australia will require captains of all planes arriving from the Americas to report on the health of passengers before receiving landing permission.

China warned citizens visiting or already in Mexico to take precautions. It has banned all direct or indirect imports of swine or pork products from Mexico and from Texas, California and Kansas, the country’s General Administration of Quality Supervision, Inspection and Quarantine said.

Indonesia, Southeast Asia’s largest economy, also banned imports of pork and edible swine products from today.

Russia, which has stopped pork imports from about 10 U.S. states, said it’s seeking more information from the U.S. on measures it’s taking to combat swine flu before lifting the ban.

Four people in France suspected of having swine flu have tested negative for the virus, an official at the Health Ministry said today.

In Brazil, the Sao Paulo state hospital Emilio Ribas has isolated a potential case, said Doctor Edenilson Eduardo Calore, head of weekend duty. The patient had been in Mexico, Calore said.

Michael Bloomberg is the founder and majority owner of Bloomberg LP, the parent company of Bloomberg News.

To contact the reporters on this story: Hans Nichols in Washington at Hnichols2@bloomberg.net; Tom Randall in New York at trandall6@bloomberg.net.

Last Updated: April 27, 2009 17:41 EDT