In addition, hospital emergency rooms continue to fill up with patients who have "swine flu jitters," hand sanitizers are disappearing from drug store shelves and airlines are taking unusual precautions. British Airways is handing out masks to Mexico-bound passengers. Lufthansa is putting a doctor on flights to Mexico. And Alaska Airways is eliminating pillows, hoping that will help halt the spread of germs.
The jitters persist despite efforts to tamp down fears about the potency of the H1N1 virus that has been dubbed swine flu.
And there is one worrisome pattern. While most flus strike the very young and the elderly, this virus has taken its toll on older children and young adults. Of the 30 people hospitalized in the United States with swine flu, many fit this category. And nine of the 19 deaths in Mexico attributed to swine flu were people between the ages of 21 and 39.
In the United States, the virus claimed the life of a toddler in Texas last month.
The virus spread to Colombia in the first confirmed case in South America, a fact that has worried health officials, since the flu season is about to begin on the continent. Experts are worried that typical winter flus could combine with swine flu there, creating a new strain that is more contagious or dangerous.
WHO Director-General Margaret Chan told reporters Monday that the organization would not move its alert level to Phase 6 -- meaning a pandemic has officially begun -- until "we see in another region outside North America showing very clear evidence of community-level transmission."
The Associated Press contributed to this story.