Following an outbreak of E. coli that is said to be linked with McDonald’s Quarter Pounder burgers, the US Centers for Disease Control and Prevention (CDC) has issued a food safety alert.

So far, 49 cases of illness have been reported between 27 September and 11 October across 10 states: Colorado, Iowa, Kansas, Missouri, Montana, Nebraska, Oregon, Utah, Wisconsin, and Wyoming.

The CDC has reported that most cases have come from Colorado and Nebraska, with ten cases resulting in patients being admitted to hospital, including a child who had hemolytic uremic syndrome—a serious condition that can cause kidney failure—as well as the death of an older person.

Although most E. coli bacteria are harmless, some can make people very sick with symptoms such as diarrhoea, urinary tract infections, pneumonia, sepsis, and other illnesses.

More severe infections can lead to life-threatening conditions, such as hemolytic uremic syndrome (HUS), high blood pressure, chronic kidney disease, and neurological problems.

It is currently unknown which ingredient is making people ill, but everyone interviewed in connection with the outbreak reported eating at McDonald’s before falling ill, with most specifically mentioning eating a Quarter Pounder.

McDonald’s statement

McDonald’s is working with public health officials to determine the contaminated ingredient, with investigators believed to be focusing on the slivered onions and beef.

In an official statement, McDonald’s confirmed they have paused the distribution of all slivered onions in the impacted area due to preliminary findings from the investigation, indicating “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.”

The fast-food chain is also temporarily removing the Quarter Pounder from its restaurants in the affected states, adding: “We take food safety extremely seriously, and it’s the right thing to do.”

All other menu items across these stores, including other beef products, are unaffected and available for purchase.