Mexican and U.S. health officials searched on Saturday for signs an outbreak of a new flu strain is spreading further, after it killed up to 68 people in Mexico and infected eight in the United States.
As Mexico shut schools and museums and axed public events, global health officials stopped short of declaring a pandemic.
But they warned more cases could come to light, making up a major outbreak, as the flu spreads between people and infected some individuals who had no contact with one another.
The World Health Organization said the virus from 12 of the Mexican patients was the same genetically as a new strain of swine flu, designated H1N1, seen in eight people in California and Texas who later recovered.
The Mexican government said the flu had killed 20 people and it may also be responsible for 48 other deaths. In all, 1,004 suspected cases have been reported nationwide.
Health Minister Jose Angel Cordova, speaking on the evening television news, encouraged people to avoid crowds and wear face masks, noting there was no guarantee that going to get a flu vaccine would help against the new strain.
He said the death rate appeared to have steadied and hospitals in the past few days had not seen the exponential rise in the number of people infected that many had feared.
Genetic analysis shows the flu strain is a never-before-seen mixture of swine, human and avian viruses.