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Flu outbreak may be smaller than feared

By Denise Grady and Liz Robbins
New York Times / May 2, 2009
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The swine flu outbreak in Mexico may be considerably smaller than originally feared, test results released there yesterday indicate.

Of 776 suspected cases that were tested, only 358 people turned out to have the virus, officially known as influenza A (H1N1), Mexican health officials reported at a news conference.

Mexico had reported about 2,500 suspected cases as of yesterday, but the number of real cases could turn out to be less than half the suspected number if further testing follows the same pattern as the original round. Officials said that the tests were being done quickly, and that 500 more would be completed.

The materials needed to perform the test were provided to Mexico by the US Centers for Disease Control and Prevention.

Officials at the centers declined to say what the new numbers might mean.

"We are continuously assessing new information, but it is still too early to draw conclusions about the extent of the spread of this new virus in Mexico or the severity of disease caused by it," Dr. Nancy Cox, chief of the influenza section, said by e-mail, when asked to comment on the test results.

Officials at the World Health Organization, which has declared the outbreak Phase 5 of the six phases in its pandemic-preparedness plan, declined to comment beyond saying that the investigation into the outbreak was continuing.

But a public health and infectious disease expert from Vanderbilt University, Dr. William Schaffner, said the test results were "going to change, I think in a substantial way, the image of this outbreak in Mexico."

If the outbreak is much smaller than initially thought, Schaffner said, "It would, I think, enable the world's public health community to take a deep breath and continue to track the outbreak and reduce the tendency, as the WHO has been doing, to notch up on its pandemic scale."

If the testing also shows that the disease has caused fewer deaths than the 170 or so suspected, Schaffner said, it might resolve a question that has been puzzling health experts since the outbreak began: why did the disease appear to be so much more severe in Mexico than in the United States? In the United States, cases have been mild and there has been only one death, that of a 23-month-old child from Mexico.

Meanwhile, the disease continued to spread to other countries and was confirmed in more American states yesterday.

But health officials around the world cautioned against panic even as they began making preparations for a vaccine that would be available in late summer or fall.