The number of people infected by the E. coli outbreak tied to McDonald’s Quarter Pounder hamburgers increased to 75 from 49, the US Food and Drug Administration said on Friday.

Of the 61, on whom information was available, the health regulator said 22 persons have been hospitalised. Two of them have developed hemolytic uremic syndrome, a serious condition that can cause kidney failure.

The E. coli O157:H7 strain that has caused the death of one person is said to cause “very serious disease”, especially for the elderly, children and people who are immunocompromised.

The world’s largest burger chain temporarily paused serving the Quarter Pounder in a fifth of its 14,000 US restaurants that were impacted, the company had said on Wednesday.

Slivered onions used in the Quarter Pounder was the likely source of the outbreak and it was supplied by a single supplier that serves three distribution centers, initial findings of the FDA as well as the company showed.

Taylor Farms was the supplier for the affected locations and McDonald’s has initiated a voluntary recall, the company and the agency have said. The supplier also has recalled several batches of yellow onions produced in a Colorado facility.

McDonald’s said late on Friday that onions from  Taylor Farms’ Colorado facility were distributed to about 900 of its restaurants in Colorado, Kansas, Wyoming, and portions of other states in the region.

The company said it had also decided to stop sourcing onions from  the facility indefinitely.

The US Department of Agriculture said late on Wednesday even though onions are the likely suspects, one of its state partners is testing samples of the beef used in the burger for E. coli.

As of October 24, the outbreak has affected Colorado, Kansas, Utah, Wyoming, Iowa, Missouri, Montana, Nebraska, New Mexico, Oregon, Wisconsin, Washington and Michigan. Colorado reported 26 infections, the Centers for Disease Control and Prevention said on Friday.

Due to the product actions taken by McDonald’s and Taylor Farms, the risk to the public is very low, the CDC said.

Other major US fast food chains such as Taco Bell owner Yum and Restaurant Brands unit Burger King were pulling fresh onions out of their menu items. These restaurant chains also source from Taylor Farms.

Shares of McDonald’s closed down about 3% on Friday.

“We continue to believe that more infections are possible in the near term, and the greatest risk to investor, is the continuous negative news cycle,” BTIG analyst Peter Saleh said.