By MARK STEVENSON and DAVID KOOP (Associated Press Writer)
From Associated PressMay 12, 2009 3:38 AM EDT
MEXICO CITY – The swine flu virus was confirmed on Tuesday to have spread to more countries as scientists estimated the new strain could have sickened 23,000 people in Mexico alone before anyone realized it was an epidemic.
Mexican Health Secretary Jose Cordova said his nation’s shutdown of schools – which was lifted in most of the country’s 31 states Monday – had averted an avalanche of cases.

“It would have been difficult for us to have controlled this epidemic,” Cordova said, according to a statement released his office late Monday. It said Mexico had 56 deaths and 2,059 confirmed cases of swine flu.


The analysis in Science suggests there are many more cases than those confirmed by laboratories – anywhere from 6,000 to 32,000 cases in Mexico as of April 23. The flu has since spread around the world, and the study said it appears to be substantially more contagious than normal, seasonal flu.

Researchers also compared the DNA of the viruses in 23 confirmed cases, and came up with an estimate of Jan. 12 for their earliest common ancestor – presumably when person-to-person transmission began. But with everything that isn’t known, they said it could have been anywhere from Nov. 3 to March 2.

The researchers said the 2009 H1N1 flu appears to be about equal in severity to the flu of 1957 and less severe than the deadly 1918 version.

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