The World Health Organization says it has noticed mutations in the bird flu virus now spreading in China, but says the risk of the disease spreading easily between people remains low. In a press briefing Wednesday, the U.N. health agency said in about 7 percent of the people infected with the H7N9 strain of bird flu, scientists have identified genetic changes suggesting the viruses are resistant to Tamiflu, the recommended treatment for the disease and the drug that is being stockpiled worldwide in preparation for a flu pandemic.