The CDC has started tracking the novel virus using the surveillance system used for seasonal influenza, called FluView.

Of the three confirmed deaths from complications of swine flu in the U.S. — a man in his 30s, a toddler and a pregnant woman — each suffered from several other illnesses when they were infected with the virus.

Last week, the CDC also described the symptoms experienced by Americans with swine flu. About 90 percent reported fever, 84 percent reported cough and 61 percent reported a sore throat — all similar to what’s seen with seasonal flu. But about one in four cases have also involved either vomiting or diarrhea, which is not typical for the normal flu bug.

It’s possible the virus is spreading not only through coughed and sneezed droplets — as with seasonal flu — but also through feces-contaminated hands, said Dawood.

“This is a new virus and we’re still learning how transmission occurs,” she said.

About 10 percent of the Americans who got swine flu had traveled to Mexico and likely picked up the infection there.