In a swift response to a potential health crisis, fast-food chains across the nation began pulling fresh onions from their menus on Thursday after an alarming E. coli outbreak was traced back to McDonald’s. The outbreak has sickened 49 individuals and resulted in one tragic death, prompting urgent action from industry leaders.

Restaurant Brands International, the parent company of Burger King, and Yum Brands, which oversees KFC, Pizza Hut, and Taco Bell, are taking precautionary measures by removing fresh onions from various menu items. A spokesperson for Burger King confirmed that about 5% of their locations have already eliminated onions from their offerings as a safety precaution.

According to McDonald’s, the sliced onions linked to the outbreak were supplied by Taylor Farms, a significant player in the food supply chain. While Taylor Farms has yet to issue a public statement, they have recalled several batches of yellow onions produced in a Colorado facility, as detailed in a recall memo from US Foods, one of the largest food service suppliers in the country.

Interestingly, although Burger King sources approximately 5% of its onions from Taylor Farms, the company has not yet received any alerts from health authorities regarding illnesses associated with their restaurants. Yum Brands has also opted to remove onions “out of an abundance of caution,” showcasing a proactive approach in safeguarding their customers.

On Wednesday, the U.S. Department of Agriculture indicated that fresh onions are the likely culprit behind the outbreak. The Food and Drug Administration (FDA) is currently investigating all possible sources but has not definitively identified the cause.

E. coli outbreaks have historically posed significant challenges for major fast-food chains, leading to consumer fears and plummeting sales. Regulatory scrutiny is also intensifying as officials explore whether McDonald’s beef patties might be affected. However, it’s worth noting that E. coli is neutralized in properly cooked beef, and the concern primarily arises from the raw, slivered onions that accompany popular menu items like the McDonald’s Quarter Pounder.

In response to the situation, McDonald’s has removed the Quarter Pounder from approximately 20% of its U.S. locations, particularly in states including Colorado, Kansas, Utah, and Wyoming, as well as parts of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma.

Maria Gonzales, the on-duty manager at a Burger King in Longmont, Colorado, confirmed, “We’ve been told by corporate to not use any onions going forward for the foreseeable future. They’re off our menu.” This kind of decisive action illustrates the seriousness with which these chains are treating the situation.

McDonald’s is keenly aware of the potential fallout from this outbreak, particularly given the historical context. Past E. coli outbreaks at other chains, such as Chipotle Mexican Grill in 2015 and Jack in the Box in 1993, resulted in significant declines in sales lasting several quarters.

In light of these developments, David Tarantino, an analyst at Baird Equity Research, has downgraded McDonald’s shares to “neutral,” expressing concern that reports of the E. coli outbreak could severely impact consumer sentiment and subsequently hurt U.S. comparable-store sales.

As the investigation continues and the fast-food industry navigates this challenge, one thing is clear: consumer safety must remain the top priority, and the swift actions taken by these chains reflect their commitment to protecting their customers from harm.