A Colorado man who fell ill from E. coli after eating a McDonald’s Quarter Pounder filed a lawsuit against the fast-food titan Wednesday.

Plaintiff Eric Stelly, a Greeley resident, bought the Quarter Pounder at his local McDonald’s on Oct. 4 and got sick two days later before being diagnosed with the bacteria by doctors on Oct. 8. In his complaint, Mr. Stelly asked for damages of over $50,000 on three counts of product liability, negligence and breach of warranty as well as for a jury trial.

“The McDonald’s E. coli outbreak will be one of the most significant food poisoning outbreaks this year. Through this lawsuit and others, we will make sure that all of the victims are fully compensated for their losses, that their voices are heard, and that McDonald’s and its suppliers permanently fix the health violations that caused the food to become contaminated with E. coli,” food safety attorney Ron Simon, who is representing Mr. Stelly and others, said in a press release.

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Chicago-based McDonald’s hasn’t responded to a request for comment.

The exact cause of the outbreak hasn’t been determined, but McDonald’s said in a release Tuesday that the likely cause was slivered onions used in Quarter Pounders sourced from a single supplier that delivers to three of the eatery’s distribution centers.

Restaurants in the outbreak area have removed the slivered onions, and Quarter Pounders have been taken off the menu across Colorado, Kansas, Utah and Wyoming as well as parts of Oklahoma, Nevada, New Mexico, Nebraska, Montana, Missouri, Iowa and Idaho. This accounts for about 20% of McDonald’s U.S. stores, according to The Associated Press.

“We take food safety extremely seriously, and it’s the right thing to do. … We will continue to work with the Centers for Disease Control and Prevention and are committed to providing timely updates as we restore our full menu,” McDonald’s said.

Taylor Farms, a McDonald’s supplier, has recalled the yellow onions produced at its Colorado facility. The company hasn’t found traces of E. coli but initiated the recall to be safe.

“Taylor Farms Colorado removed yellow onions from the market produced out of our Colorado facility. We continue to work closely with the FDA and CDC during this ongoing investigation,” the company told Bloomberg Wednesday.

The Agriculture Department’s Food Safety and Inspection Service checked McDonald’s patties to determine whether the beef could be the source of the outbreak, the Food and Drug Administration said in a release. 

An FSIS spokesperson told NBC News that a probe led officials to zero in on the onions as the likeliest source of the bacteria.

“While the slivered onions are the likely source, FSIS continues to verify the safety of the ground beef used. A state partner has collected samples from the ground beef patties for testing,” the spokesperson added.

The first confirmed case in the ongoing outbreak linked to the McDonald’s Quarter Pounder was reported on Sept. 27, according to the CDC. There have been 49 confirmed cases, 10 hospitalizations and one death across Oregon, Montana, Wyoming, Utah, Colorado, Nebraska, Kansas, Missouri, Iowa and Wisconsin.

The CDC noted that more recent cases may have not been reported because it usually takes three to four weeks to confirm that a patient’s illness is linked to a wider outbreak.

Symptoms of people infected with E. coli include diarrhea, stomach cramps, vomiting and dehydration.