Health officials in the United States (US) are investigating a multi-state outbreak of E. coli infections linked to McDonald's Quarter Pounder burgers.

The Centers for Disease Control and Prevention (CDC) reported 49 cases across 10 states connected to the burgers.

The CDC stated: “Most sick people are reporting eating quarter pounder hamburgers from McDonald’s and investigators are working quickly to confirm which food ingredient is contaminated.”

McDonald's has already pulled ingredients for these burgers in certain states, making them unavailable for sale, according to the CDC.

The CDC is collaborating with the Food and Drug Administration (FDA), the US Department of Agriculture (USDA), the Food Safety and Inspection Service (FSIS), and other health officials in this ‘fast-moving outbreak investigation’.

McDonald’s is also working with investigators to pinpoint which ingredient in the Quarter Pounders is causing the illnesses. The company has temporarily stopped using fresh slivered onions and Quarter Pounder beef patties in some states while the investigation continues.

Early data from the FDA suggests onions may be the source of the outbreak linked to the McDonald's burgers, according to the CDC.

The first case was reported on September 27, affecting people aged 13 to 88 years. The CDC stated on Tuesday, October 22, that ‘of 28 people with information available, 10 have been hospitalised, and one person developed hemolytic uremic syndrome, a serious condition that can cause kidney failure’.

The CDC also reported one fatality, involving an older adult in Colorado, and warned that the ‘true number of sick people in this outbreak is likely much higher than the number reported’ and that the outbreak might extend beyond the known states.

In an internal message, McDonald's North America chief supply chain officer Cesar Pina said: “Serving customers safely in every single restaurant, each and every day, is our top priority and something we’ll never compromise on."

Pina also informed employees that McDonald's was ‘taking swift and decisive action following an E. coli outbreak in certain states’.

He added: “The initial findings from the investigation indicate that a subset of illnesses may be linked to slivered onions used in the quarter pounder and sourced by a single supplier that serves three distribution centres.

“As a result, and in line with our safety protocols, all local restaurants have been instructed to remove this product from their supply and we have paused the distribution of all slivered onions in the impacted area.

“Out of an abundance of caution, we are also temporarily removing the quarter pounder from restaurants in the impacted area, including Colorado, Kansas, Utah and Wyoming, as well as portions of Idaho, Iowa, Missouri, Montana, Nebraska, Nevada, New Mexico, and Oklahoma.”

Pina emphasised that McDonald’s takes ‘food safety extremely seriously’.