(AP) -- The swine flu epidemic may seem mild now, with relatively few deaths even as the virus infects thousands in at least 33 countries. But experts worry it could mutate into something more dangerous - making the question of who should get antiviral therapy ever more important.
The World Health Organization said Tuesday that countries should save antiviral drugs for those patients most at risk, and the U.S. Centers for Disease Control and Prevention added that pregnant women in particular should take the drugs if they are diagnosed with swine flu - even though the effects on the fetus are not completely known.
European countries have been using antiviral drugs such as Tamiflu and Relenza much more aggressively than the United States and Mexico - administering it whenever possible in an attempt to contain the virus before it spreads more widely.
Instead, the WHO recommends that antivirals be targeted mainly at people already suffering from other diseases or complications - such as pregnancy - that can lower a body's defenses against flu, WHO medical expert Dr. Nikki Shindo said.
Pregnant women are more likely to suffer pneumonia when they catch flu, and flu infections raised the risk of premature birth in past epidemics. A pregnant Texas woman who had swine flu died last week, and at least 20 other pregnant women have swine flu, including some with severe complications.
For all these reasons, risks from the virus are greater than the unknown risks to the fetus from Tamiflu and Relenza, said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.
"We really want to get the word out about the likely benefits of prompt antiviral treatment" for pregnant women, she said.
Mexico is now giving Tamiflu to anyone who has had direct contact with a person infected with swine flu, Health Secretary Jose Angel Cordova said. And now that schools are back in session, authorities plan to give Tamiflu to any children who show symptoms and are suspected of being infected.
CDC officials said the swine flu may seem to be mild now, but they worry the virus will mutate into something more dangerous - perhaps by combining with the more deadly but less easily spread bird flu virus circulating in Asia and Africa.
Another concern is that it will combine with the northern winter's seasonal H1N1 virus. While not unusually virulent, it was resistant to Tamiflu, and health officials worry that it could make the new swine flu resistant to Tamiflu as well.
The nearly 6,000 confirmed cases worldwide so far have included 63 deaths, and Mexico's death toll rose by two on Tuesday to 58, with 2,282 confirmed infections. But Cordova said the worst appears over - and the more cases the country confirms, the less deadly the virus appears. The increasing toll reflects a testing backlog, Cordova said, with the last confirmed case on May 8.
The U.S. has the world's highest caseload, at more than 3,000 infections in 45 U.S. states, but many countries have focused their energy on containing the spread from Mexico, rather than the U.S. Cuba, Thailand and Finland reported their first cases Tuesday, all in people who had returned from Mexico, and criticism of Mexico's handling of the crisis continues.
Cuba's first case - a Mexican student attending a Cuban medical school - came despite strict restrictions on flights and travelers, prompting former president Fidel Castro to accuse Mexico of hiding the epidemic until after President Barack Obama visited last month.
Mexico has denied hiding anything - and the timeline supports this: Obama's April 16 visit came a week before Canadian and U.S. scientists identified swine flu in Mexican patients, at which point Mexico quickly imposed an unprecedented shutdown of most aspects of public life for days.
"The response by Mexico's health care system and the country's transparency in the way it conducted itself has allowed all nations ... to be able to take preventive measures in a timely manner so they could combat this illness," President Felipe Calderon said Tuesday.
China said it has tracked down and quarantined most passengers who shared flights with the mainland's first known swine flu sufferer - a Chinese graduate student from the U.S. who is said to be improving.
"We must attach great importance to the fact that the flu epidemic is still spreading in some countries and regions, and that China has discovered one case," said President Hu Jintao.
About 260 people were quarantined in Beijing, including 70 foreigners, the China Daily reported. In Sichuan province, the government said another 95 people were being isolated.
With the virus now spreading worldwide, Swiss pharmaceuticals company Roche Holding AG announced it is donating enough Tamiflu for 5.65 million more people to WHO. A further 650,000 packets containing smaller doses of the drug will be used to create a new stockpile for children.
At the start of the outbreak, Mexico had enough Tamiflu for 1 million people, and has since received more, building reserves of 1.5 million courses.
Each country's health experts must decide if infected people should immediately be treated with antivirals, Shindo said - a decision that also must take into account how many antivirals are available.
"As part of pandemic preparedness plans, we urge countries to plan for prioritization," Shindo said.
Mexico's overburdened health system has been strained. Dozens of government doctors and nurses marched and blocked streets in the Gulf coast city of Jalapa to demand higher pay and better working conditions.
Mexico also is trying to revive its economy after the epidemic pummeled tourism, the country's third-largest source of legal foreign income. Cordova said there have been no swine flu cases in five top Mexican vacation spots, including Los Cabos, Puerto Vallarta, Cozumel, Mazatlan and Zihuatanejo.
But with incoming flights virtually empty of tourists, Tourism Secretary Rodolfo Elizondo said a $90 million publicity campaign would focus on encouraing Mexicans to vacation at home.
Promoting trips by foreigners now, he said, "would be like throwing money away."
Associated Press writers Michael Stobbe in Atlanta; Maria Cheng in London; and Gillian Wong in Beijing contributed to this report.
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