A food poisoning outbreak linked to McDonald’s last year has taken a sinister new twist.

One person died and 104 got infected by E. coli they caught from Quarter Pounder hamburgers that contained onions contaminated with the deadly bacteria. 

The outbreak was declared over in December but this week, for the first time, E. coli was newly linked to the colon cancer epidemic in young Americans.

There is no evidence the McDonald’s outbreak is linked to any cancer cases, but experts said it highlights that a growing problem of food contamination in the US could be having devastating consequences on people’s health. 

Escherichia, or E. coli, is a bacteria found in the intestines of humans and animals. It can also be present in the environment, including contaminated water, food, and on surfaces.

According to the CDC’s National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), outbreaks, hospitalizations and deaths from E. coli are on the rise. There were 112 outbreaks of E. coli in 2023, compared to 84 a decade ago.

Final numbers for 2024 haven’t been released yet, but the NCEZID reports there were 37 outbreaks of one strain of E. coli – STEC, the one behind last year’s deadly McDonald’s outbreak.

Experts say the rise in antibiotic-resistant bacteria, along with mass production and factory farming are driving outbreaks as they increase the chances of contamination and decrease the efficacy of drugs to fight the infection. 

The onions from McDonald’s Quarter Pounder burgers were at the center of an investigation into an E.coli outbreak last year (stock image)

E. coli is often in contaminated water that has been tainted with feces, which then may be used to irrigate crops or clean farming or manufacturing equipment, exposing the food to the bacteria. 

Common culprits of E. coli are raw milk, romaine lettuce, spinach and produce like apples and cucumbers, as well as undercooked ground beef.

Most strands of E. coli are harmless, though six produce toxins: siga toxin-producing (STEC), enterotoxigenic (ETEC), enteropathogenic (EPEC), enteroinvasive (EIEC), enteroaggregative (EAEC) and diffusely adherent (DAEC). 

Once E. coli enters the body, it travels to the colon where the bacteria disrupts the lining of the intestines and produces toxins that cause bloody diarrhea, vomiting, severe stomach cramps, fever and hemolytic uremic syndrome (HUS) – a deadly kidney condition.

A new study this week from researchers at the University of California San Diego believe they’ve found a potential link between E. coli and colon cancer.

By analyzing DNA from young colon cancer patients, the team found unique genetic changes in their digestive tracts that appear to raise the risk of tumors forming — likely triggered during childhood, when the body is still developing. 

They also detected traces of colibactin, a cancer-linked toxin produced by certain strains of E. Coli, lurking in tumors from patients under 40.  

The study, published Wednesday in the journal Nature, looked at the DNA of 981 colon cancer tumors in patients who were either under 40 or over 70 in 11 countries, including the US and UK.

They found colibactin leaves behind specific patterns of DNA mutations that were 3.3 times more common in early-onset cases than in those diagnosed after the age of 70. 

These mutations were also most common in countries with high rates of early-onset colon cancer, such as the US and UK.

The study is the first to show these cancer-driving mutations are significantly more common in younger patients, suggesting a unique link between childhood exposure and early-onset colon cancer. 

Ludmil Alexandrov, senior author and professor of cellular and molecular medicine at the University of California San Diego, said the team’s finding ‘reshapes how we think about cancer.’

He added: ‘These mutation patterns are a kind of historical record in the genome, and they point to early-life exposure to colibactin as a driving force behind early-onset disease.

‘This reshapes how we think about cancer. It might not be just about what happens in adulthood — cancer could potentially be influenced by events in early life, perhaps even the first few years.’

Dr Cedrek McFadden, a colon and rectal surgeon and associate professor of surgery at the University of South Carolina School of Medicine Greenville, told DailyMail.com: ‘The idea that a toxin from certain strains of E. coli — colibactin — could leave behind a cancer-linked fingerprint in the DNA of younger patients is eye-opening. 

‘It reinforces something we’re seeing more and more: early-onset colon cancer isn’t just happening earlier, it may actually be a different disease with unique triggers.

‘If that trigger includes E. coli exposure during childhood, that’s a big deal — especially with how often we’re seeing food safety issues make headlines. 

‘It’s no longer just about avoiding a bad stomach bug. We’re now talking about possible long-term consequences, including cancer risk.’

While E. coli can come from many sources, a common culprit is fast food, with outbreaks occurring at favorites such as McDonald’s, Burger King, Taco Bell and Jack in the Box. 

Last year, investigators at the CDC said the chopped yellow onions used in McDonald’s Quarter Pounders, produced by California-based Taylor Farms, were the likely source of the chain’s E.coli outbreak.

The burgers were pulled from menus for several weeks but have since returned. 

A total of 104 people were infected across 14 states between September and October 2024. Of those, 34 people were hospitalized, four people developed HUS and one person died. 

Burger King, Taco Bell, KFC and Pizza Hut all also stopped using onions as a ‘proactive’ measure amid the outbreak. 

Escherichia, or E. coli, is a bacteria found in undercooked ground beef, raw milk, romaine lettuce, spinach and produce like apples and cucumbers 

Colorectal cancer, long considered a disease of old age, is increasingly striking people in their 20s, 30s and 40s in a phenomenon that has baffled doctors. 

The number of people under 50 being diagnosed with colon cancer is increasing worldwide, according to a major global study published last year.

An increase in rates was reported in 27 of the 50 countries examined by US researchers, with the greatest annual increases seen in New Zealand (four percent), Chile (four percent) and England (3.6 percent).

According to the latest data, early-onset colon cancer diagnoses in the US are expected to rise by 90 percent in people 20 to 34 years old between 2010 and 2030.

In teens, rates have surged 500 percent since the early 2000s.

Experts have hypothesized that everything from improved screening, ultra-processed foods, environmental toxins and an off-balance microbiome could be to blame for the increase. 

Dr Pashtoon Kasi, medical director of GI medical oncology at City of Hope Orange County in California, told DailyMail.com: ‘We are what we eat, as they say… Dietary or lifestyle changes that can contribute to bad changes in the “microbiome” could be contributing to this rise of young onset colorectal cancers. 

‘It’s important to focus on healthy dietary and lifestyle behaviors.’ 

In advice for people to fend off E. coli and possibly protect themselves against colon cancer, Dr McFadden told this website: ‘My advice to the public is to take food safety seriously: wash your produce, cook meat thoroughly, and stay on top of recall alerts. 

‘And for public health leaders, this might be a wake-up call to tighten oversight and invest in more proactive protections — especially when kids are involved.’