You might have heard about the E. coli outbreak that worried McDonald's fans. Well, the fast-food giant is bringing back Quarter Pounders to all restaurants soon. Here's what happened.

Last week, the Centers for Disease Control and Prevention (CDC) warned people about getting sick after eating Quarter Pounders at McDonald's. The outbreak affected 75 people across 13 states, with one sad death. Most of the cases were in Colorado.

Experts weren't sure what was causing the illness. Some thought it might be the beef patties or the onions on the Quarter Pounder. Then, the Colorado Department of Agriculture tested McDonald's beef patties and found no E. coli. This made McDonald's confident that the beef isn't the problem.

So, McDonald's is asking their beef suppliers for fresh patties. But the restaurants that got onions from a certain supplier in Colorado will only sell Quarter Pounders without onions for now.

The Food and Drug Administration (FDA) and CDC are still investigating, trying to find the exact cause. They're checking onions too. Taylor Farms, the onion supplier, stopped selling yellow onions just in case.

McDonald's wants you to know they're sorry for the trouble and promise to make things right.

Quarter Pounders Back on Menus: What You Need to Know

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