McDonald's responds to E. coli outbreak, one-fifth of US stores remove "foot twos"

McDonald's is stepping up efforts to contain the fallout from a severe E. coli infection caused by Onions in its popular "Foot three two" hamburger.

McDonald's said Wednesday that less than a fifth of its more than 13,000 U.S. restaurants have the Quarter Pounder burger on display, and it could take weeks to get it back on shelves. The burger, which typically sells a million copies every two weeks in the United States, is one of McDonald's star products.

The Centers for Disease Control and Prevention (CDC) announced Tuesday that it has launched an investigation into a series of illnesses in 10 states between Sept. 27 and Oct. 11. The accident sickened dozens of people, resulting in one death and 10 hospitalizations. McDonald's shares fell 5 percent Wednesday as investors tried to figure out how much the crisis was affecting the burger chain.

McDonald's said it is too early to determine the impact of the infection on sales and that the company is working with the CDC and other government agencies to eradicate the source of the disease and keep customers safe. The company believes the contamination was at the supplier's fault, not the food preparation process at its restaurants.

The CDC warned that the true number of infections could increase in the coming weeks as the investigation into the source of the E. coli spread. The bacteria causes infections in the body and can be spread through raw or undercooked meat or contaminated foods such as fruits and vegetables. The agency said the number of cases could continue to rise because it takes three to four weeks to determine if a patient was involved in the accident.

"This is definitely a very active investigation and means we expect to find more cases," said Rachel Herlihy, an epidemiologist with the Colorado Department of Public Health and Environment.

Bill Marler, a Seattle-based food safety lawyer, said the number of infections could climb from 50 to at least 500 and that "we probably haven't seen the end of this infection."

McDonald's said it was first notified of the accident by government agencies late last week. After the CDC made the incident public Tuesday, McDonald's promised to take "swift and decisive action."

It is not clear when the company made the decision to remove the "foot three two" burger from some restaurants, or when the chain communicated the issue to its franchisees.

A Colorado restaurant contacted by Bloomberg said it was notified on Sunday to stop serving products containing Onions. Other restaurants said they only learned of the incident on Tuesday. On Wednesday, the "foot three two" burger had disappeared from some food delivery apps in several U.S. states.

McDonald's pointed to Onions as a possible culprit, but did not rule out beef as a potential source of contamination. The company said Wednesday that the suspected onion came from a single supplier, while the beef patties came from multiple suppliers and were cooked inside the restaurant.