The number of people infected by the E. coli outbreak tied to McDonald’s Quarter Pounder hamburgers increased to 75 from 49, U.S. Food & Drug Administration officials said today.

Of the 61 on whom information was available, the health regulator said 22 persons have been hospitalized. 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 U.S. restaurants that were impacted, the company had said on Wednesday.

(State Department of Health officials said today that they have no current investigations into McDonald’s locations in the state. They said there have been no recent E. Coli cases reported following consumption of McDonald’s food and that there have been no signs of an increase in E. Coli cases in Hawaii.)

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 said. The supplier also recalled several batches of yellow onions produced in a Colorado facility.

The U.S. 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 Oct.24, the outbreak has affected Colorado, Kansas, Utah, Wyoming, Iowa, Missouri, Montana, Nebraska, New Mexico, Oregan, Wisconsin, Washington and Michigan. Colorado reported 26 infections.

Due to the product actions taken by McDonald’s and Taylor Farms, the risk to the public is very low, the Centers for Disease Control and Prevention said today.

Other major U.S. 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 were down about 3% in late-day trading on Wall Street.

“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.

Star-Advertiser staff contributed to this report.