McDonald's E. coli outbreak expands to 75 people. How dangerous is it?

Dozens of people across 13 states have become sick after eating McDonald’s Quarter Pounders contaminated with E. coli.

At least 75 people fell ill from the bacterial infection and one person died in Colorado from the O157:H7 strain of E. coli, the Centers for Disease Control and Prevention said Friday. McDonald’s attributed the illnesses to slivered onions, and the Food and Drug Administration indicated that onions might have been the source of the outbreak.

What's happening with investigation?

Federal regulators are determining whether slivered onions or beef patties in Quarter Pounder burgers caused the outbreak, the CDC said.

Based on information available for 61 of the 75 people who got sick, the CDC said Friday 22 had been hospitalized and two developed a serious condition from the bacteria that can cause kidney failure. These cases began occurring in late September and continued through Oct. 10.

Of 42 people interviewed by officials, all said they'd eaten at McDonald's, and 39 said they'd eaten a beef hamburger. Among the 36 people who remembered which specific beef burger they'd eaten, 31 said they had a Quarter Pounder.

Earlier this week, McDonald’s pulled its Quarter Pounders and slivered onions from menus in several states. Taylor Farms, which supplied slivered onions for affected McDonald's locations, initiated a recall of yellow onions, the CDC said.

In a statement, Taylor Farms said it "preemptively" recalled yellow onions from its Colorado facility that had been sent to select foodservice customers.

"We continue to work with CDC and FDA who are investigating the source of the outbreak," the statement said. "All Taylor Farms products in the market today are safe to consume."

E. coli outbreaks sometimes occur in the U.S., and the bacteria ends up in the U.S. food supply in products including frozen foods and fresh vegetables, according to the University of California, Davis, Health.

Here are other key facts to know about E. coli:

What is E. coli?

Escherichia coli is a bacteria that exists in food and water and in people's and animals' intestines, as a healthy part of the intestinal tract, the CDC said.

Different types of E. coli trigger different bodily responses. Some forms of the bacteria can make people sick.

How do people get infected with E. coli?

People can get infected through contaminated food or water, the CDC said. They can also become sick after contact with animals, animal excrement, animals' living environments or the excrement of a person infected with E. coli.

The Shiga toxin infection is often transmitted through contaminated foods, particularly leafy greens and ground beef, as well as through unsafe water, the CDC said. Contact with infected animals, especially cattle, and excrement from an infected person are also possible sources.

People from high-income countries are more likely to become sick from the bacteria. The Cleveland Clinic said the U.S. sees approximately 265,000 infections of Shiga toxin-producing E. coli each year, making it the most common cause of outbreaks and infections.

What are typical symptoms after you've ingested E. coli?

In its update on the McDonald’s cases, the CDC said most infected people with Shiga toxin-producing forms of E. coli like the one found in these individuals experience severe stomach cramps, diarrhea that is often bloody and vomiting. In some cases, people develop serious kidney issues that require hospitalization.

Symptoms typically begin three to four days after consuming food or beverages containing the bacteria.

How to avoid contact with E. coli?

The FDA said people who have eaten at McDonald’s and have symptoms should contact their health providers.

Overall, the FDA says you can prevent foodborne illness by taking sanitary precautions at home, by washing hands with warm water and soap before and after touching raw food or after touching contaminated items such as diapers or cleaning surfaces.

The federal agency also recommends washing items that have come into contact with raw food, such as the inside of refrigerators or cutting boards. You can sanitize them with a tablespoon of chlorine bleach for every gallon of hot water and dry surfaces with a clean cloth or paper towel.

People should wipe up spills in the fridge immediately. People with pets can take precautions to avoid cross-contamination when preparing their animals' food and should wash their hands after touching animals.

People should also cook meat thoroughly to 160 degrees and avoid raw milk or other unpasteurized items.

(This story was updated to add new information.)

This article originally appeared on USA TODAY: McDonald's Quarter Pounder E. coli outbreak: 75 infected in 13 states