Last week, the Centers for Disease Control and Prevention (CDC) reached out to McDonald's about a potential E. coli outbreak. At first, the number of cases was smaller, but as of Tuesday, it had grown to 49 cases with one fatality across 10 states. The outbreak is linked to McDonald's Quarter Pounder burgers.

Once notified, McDonald's started working with the CDC, USDA, and FDA. By Tuesday afternoon, when the CDC issued its advisory, McDonald's had already decided to stop selling Quarter Pounder burgers in affected areas. About a fifth of its U. S. restaurants are not selling these burgers right now.

Out of 18 people interviewed with confirmed cases, 12 said they had eaten a Quarter Pounder before getting sick. This outbreak comes at a tough time for McDonald's, as they try to win back customers after years of price hikes. They had hoped a $5 value meal deal would bring people back.

McDonald's issued a statement after the CDC's advisory, saying they're removing Quarter Pounders from restaurants in affected areas. These areas include Colorado, Kansas, Utah, Wyoming, and parts of eight other states. The CDC is investigating both the beef patties and uncooked onions as potential causes.

McDonald's uses multiple beef suppliers, but the onions come from a single supplier that washes and slices them. The company has paused this supplier's distribution and asked local restaurants to remove their onion stock. The outbreak occurred between September 27 and October 11. During this time, McDonald's sells about one million Quarter Pounders in the affected region.

Investors are concerned, and McDonald's shares are down 5% in afternoon trading, as they worry about a possible sales slump.

McDonald's Faces E. coli Outbreak: A Closer Look at the Crisis

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