WHY Pizza Hut, KFC and Burger King took fresh onions off their menus?

Fast-food chains in the United States pulled fresh onions from some menus on Thursday after the vegetable was linked as the likely source of a deadly E. coli outbreak at McDonald's restaurants.

Taco Bell, Pizza Hut, KFC and Burger King were among those that took onions off the menus in some of their restaurants.

"As we continue to monitor the recently reported E. coli outbreak, and out of an abundance of caution, we have proactively removed fresh onions from select Taco Bell, Pizza Hut and KFC restaurants," parent company Yum Brands said in a statement.

McDonald's rival Burger King also said it had removed onions from nearly 5% of its locations.

Diner files lawsuit against McDonald's

McDonald's halted serving Quarter Pounder hamburgers — one of the chain's most popular items — in a fifth of its restaurants after one person died and at least 49 fell ill across 10 states.

One man in Colorado has filed a lawsuit against McDondald's after he ate a Quarter Pounder and tested positive for E. coli days later.

The lawsuit accuses McDonald's of having been negligent in its handling and care of the food, and seeks $50,000 (€46,000) in damages.

On Thursday, McDonald's said that a California-based company was the supplier of the sliced onions that have been withdrawn.

There was no immediate response from the produce company.

Restaurant Brands International, which owns Burger King, said that some 5% of its restaurants used onions distributed by the same company. The onions have since been withdrawn.

However, a spokesperson said the chain had not been contacted yet from health authorities or reported any illnesses.