McDonald’s is acting quickly to stop the spread of E. coli after an outbreak was linked to its Quarter Pounder burger. 

The Centers for Disease Control and Prevention (CDC), is on the case after many illnesses were reported, with a majority of the reports coming in from Colorado and Nebraska.

A complete map of locations regarding the outbreak is available here.

On Oct. 22 (Tue.), the CDC announced they are investigating 49 illnesses that have been linked to the menu staple after one person died and 10 were hospitalized.

The CDC believes that the “true number of sick people in this outbreak is also likely much higher than the number reported.”

READ MORE: McDonald’s French Fries Supplier Closes Plant, Fires More Than 300 People: Here’s Why

McDonald’s shared a message on their newsroom site, insisting that the American staple is “taking swift and decisive action following” the outbreak.

“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,” McDonald’s North America Chief Supply Chain Officer, Cesar Piña said. 

Piña noted that the popular burger chain is cooperating fully with the CDC, and that “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.”

READ MORE: Teens Used To Love These Chain Restaurants, But That’s Changing Fast

In several states, the Quarter Pounder has been completely removed from the menu for the time being as the company takes “food safety extremely seriously,” and feels “it’s the right thing to do.”

“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,” Piña added. 

E. coli symptoms are diarrhea, a fever higher than 102°, and in extreme cases, can include “so much vomiting that you cannot keep liquids down.”