One person has died and dozens have fallen sick following a severe E. coli outbreak linked to McDonald’s Quarter Pounder hamburgers, the US Centers for Disease Control and Prevention (CDC) said Tuesday.

The outbreak, which began in late September, has spread across 10 western states with most of the 49 cases concentrated in Colorado and Nebraska, the health agency said.

Shares in the fast food chain dropped more than 8 per cent in after-hours trading following the announcement.

Ten people have been hospitalised, including one child with hemolytic uremic syndrome - a serious condition that damages blood vessels in the kidneys.

“One older person in Colorado has died,” the CDC statement said.

All affected people carried the same strain of E. coli and reported eating McDonald’s Quarter Pounders before developing their symptoms.

While investigators have not yet pinpointed the exact ingredient causing the outbreak, they are focusing on slivered onions and beef patties - both of which have been removed from restaurants in the affected states pending further investigation.