MEXICO CITY: The H1N1 flu virus spread to more countries yesterday as scientists estimated the new strain could have sickened 23,000 people in Mexico alone before anyone realized it was an epidemic.

Fidel Castro, meanwhile, accused Mexico of hiding the epidemic until after US President Barack Obama visited last month.

Mexican Health Secretary Jose Cordova said his nation's shutdown of schools - which was lifted in most of the country's 31 states on Monday - had averted an avalanche of cases.