This story by Maggie Fox also quotes a CDC expert, Terrence Tumpey, M.D.

He told Fox that mutations let the new H1N1 virus live in the small intestine — something seasonal influenza cannot do. Although still not confirmed, this difference could explain why so many swine flu patients have stomach upsets such as nausea and diarrhea. (Emphasis added)

Reuters

“The new H1N1 influenza strain may be just a little less catching than seasonal flu, but seems a little better able to cause stomach upsets, researchers reported on Thursday.

“Genetic analysis and lab experiments with the virus show it lacks a piece of genetic material that makes ordinary flu viruses so transmissible, a team of U.S. researchers found.

“Researchers in the Netherlands, meanwhile, found it lives very well in the nose and their findings suggest it has the ability to stay around for a long time — and get worse. (Emphasis added)

“Both studies, published in the journal Science, show that H1N1 swine flu needs to be closely watched, said Dr. Terrence Tumpey of the U.S. Centers for Disease Control and Prevention.

“I think the take-home message is that we really need to keep a close eye on this virus,” Tumpey said in a telephone interview.”

Source: Reuters, July 2, 2009