"49 people from 10 states have gotten sick from the same strain of E. coli O157:H7. Most sick people are from Colorado (27) or Nebraska (9)," US  Centers for Disease Control said.

CDC said: "10 people have been hospitalized. One older person in Colorado has died."

CDC said one child is hospitalized with complications of hemolytic uremic syndrome, or HUS.

Everyone interviewed has reported eating at McDonald's before their illness started, and most specifically mentioned eating a Quarter Pounder hamburger, CDC said in the statement.

The specific ingredient linked to illness has not yet been identified, but investigators are focused on two ingredients in particular: fresh slivered onions, and fresh beef patties.

"McDonald's reported to CDC that they proactively removed the slivered onions and beef patties used for the Quarter Pounder hamburgers from stores in the affected states while the investigation continues. Quarter Pounder hamburgers in some states may be temporarily unavailable," CDC said.

McDonald's responds

McDonald's North America Chief Supply Chain Officer Cesar Piña said the food chain would never compromise on food safety.

"Across the McDonald’s System, serving customers safely in every single restaurant, each and every day, is our top priority and something we’ll never compromise on," Cesar Piña said.

"It is why we are taking swift and decisive action following an E. Coli outbreak in certain states. 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," he said.

Pina said the fast food chain has decided to remove the Quarter Pounder from restaurants in the impacted area.

"We take food safety extremely seriously and it’s the right thing to do. Impacted restaurants are receiving a stock recovery notice today and should reach out to their field supply chain manager or distribution centre with any questions," he said.

"We are working in close partnership with our suppliers to replenish supply for the Quarter Pounder in the coming weeks (timing will vary by local market). In the meantime, all other menu items, including other beef products (including the Cheeseburger, Hamburger, Big Mac, McDouble and the Double Cheeseburger) are unaffected and available. We will continue to work with the Centers for Disease Control and Prevention (CDC) and are committed to providing timely updates as we restore our full menu," he said.