LOS ANGELES, Oct. 22 (Xinhua) -- An E. coli outbreak linked to McDonald's Quarter Pounder burgers has led to 49 illnesses, including one death, in the United States, the country's national public health agency said on Tuesday.

The U.S. Centers for Disease Control and Prevention (CDC) said in a news release that 49 people infected with the outbreak strain of E. coli O157:H7 have been reported from 10 states to date, with most illnesses in Colorado and Nebraska.

Of 28 people with information available, 10 have been hospitalized, and 1 person developed hemolytic uremic syndrome, a serious condition that can cause kidney failure, said the agency. One death has been reported from an older adult in Colorado.

According to CDC's fast-moving outbreak investigation, most sick people are reporting eating Quarter Pounder hamburgers from McDonald's and investigators are working quickly to confirm which food ingredient is contaminated.

"The true number of sick people in this outbreak is likely much higher than the number reported, and the outbreak may not be limited to the states with known illnesses. This is because many people recover without medical care and are not tested for E. coli," noted the agency, adding that "recent illnesses may not yet be reported as it usually takes 3 to 4 weeks to determine if a sick person is part of an outbreak."

McDonald's said in its statement that "The initial findings from the investigation indicate that a subset of illnesses may be linked to slivered onions used in the Quarter Pounder and sourced by a single supplier that serves three distribution centers."

"As a result, and in line with our safety protocols, all local restaurants have been instructed to remove this product from their supply and we have paused the distribution of all slivered onions in the impacted area," said the fast-food giant, adding that it is also temporarily removing the Quarter Pounder from restaurants in the impacted area, including Colorado, Kansas, Utah and Wyoming, as well as portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma.

McDonald's shares dropped more than 9 percent in after-hours trading Tuesday after CDC's announcement of the E. coli outbreak. ■