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Swine Flu Spreads, But Severity and Genetics Remain Murky

Although the spread of swine flu appears to be accelerating—and the virus is beginning to dominate global headlines—the World Health Organization (WHO) stopped short of ratcheting up the pandemic alert level this weekend, although it may do so on Monday or Tuesday. The Obama Administration has declared the swine flu threat a public health emergency, however, and many countries have begun putting in place measures to stop the virus.

There are now 20 laboratory-confirmed cases of the swine flu in the United States—in California, Texas, Kansas, New York, and Ohio. The Mexican government has reported 18 lab-confirmed cases, according to WHO. Several other countries, including New Zealand and France, have reported suspected or possible cases.

At a press conference today, U.S. officials seemed intent on avoiding panic while at the same time preparing the public for the possibility of a major epidemic. “This is moving fast,” CDC Acting Director Richard Besser said at a midday press conference from the White House. “But we want you to understand that we view this more as a marathon.”

WHO has declared swine flu “a public health emergency of international concern,” the agency's flu expert Keiji Fukuda told reporters today during a teleconference from Geneva. Meeting on Saturday to discuss the situation, WHO's Emergency Committee decided that more information about the spread of the virus is needed before WHO's pandemic alert level can be raised from 3 to 4, which would signal a shift to "sustained human-to-human transmission" and "a significant increase in risk of a pandemic." The situation will be reviewed again on Tuesday, or earlier if necessary, Fukuda said.

Many questions remain about the virus. One enigma is the severity of the disease it causes. The 20 U.S. patients all had mild disease; only one was hospitalized briefly. In Mexico, however, there are at least 80 suspected deaths from the virus. Experts have repeatedly pointed out, however, that most of the Mexican cases have not been lab-confirmed and that some may have died of other causes. International teams are in Mexico to investigate the situation.

Fukuda said today that two of the virus's eight genetic elements appear to originate in a swine influenza strain common in Europe and Asia, whereas the remainder are typical of American swine flu strains. That information seemed at odds with a statement from CDC, which said on Thursday that the new swine flu strain contained genetic elements from human and avian influenza strains as well. During today's press conference, Anne Schuchat, interim deputy director for science and public health at CDC, declined to answer a question about the virus's genetic makeup.