Obesity emerges as new risk factor for severe flu

* Nine of 10 serious cases at Michigan hospital were obese

* Obesity not a known risk factor for influenza death

* Doctors can double Tamiflu dose in severely ill patients

By Maggie Fox, Health and Science Editor

WASHINGTON, July 10 (Reuters) - People who are obese but otherwise healthy may be at special risk of severe complications and death from the new H1N1 swine flu virus, U.S. researchers reported on Friday.

They described the cases of 10 patients at a Michigan hospital who were so ill they had to be put on ventilators. Three died. Nine of the 10 were obese, seven were severely obese, including two of the three who died.

The study, published in advance in the Centers for Disease Control and Prevention's weekly report on death and disease, also suggests doctors can safely double the usual dose of oseltamivir, Roche AG's (ROG.VX) antiviral drug sold under the Tamiflu brand name.

"What this suggests is that there can be severe complications associated with this virus infection, especially in severely obese patients," said CDC virus expert Dr. Tim Uyeki.

"And five of these patients had ... evidence of blood clots in the lungs. This has not been previously known to occur in patients with severe influenza virus infections," Uyeki said in a telephone interview.