The swine flu crisis is deepening internationally, with the death toll mounting to 152 in Mexico.
At least 16 countries now report confirmed or suspected infections.
The World Health Organisation has warned that the virus is now too widespread to make containment a feasible strategy.
Mexico, where the outbreak began, now suspects 1600 people are carrying the virus.
Twenty of the deaths there have been confirmed as swine flu by laboratory tests.
There are 44 confirmed cases in the United States, two in Britain, six in Canada, and two in Spain and Israel.
The EU said patients were also under observation in Denmark, Sweden, Greece, the Czech Republic, Germany, Italy and Ireland.
Tests are being carried out on individuals or groups in Brazil, Guatemala, Peru, Australia and South Korea.
Only the Mexican cases have been serious or fatal.
Origin not yet confirmed
Mexican media have speculated the flu may have originated at a pig farm in the southeastern state of Veracruz.
But Health Minister Jose Angel Cordova said the first case that alerted authorities to a possible rogue flu strain was in the southern state of Oaxaca. He said it was too early to identify the cause or geographical source of the virus.
The WHO on Monday raised its alert level to phase 4 out of a possible six.
Canada on Tuesday suspended flights to and from Mexico for 48 hours.