The United States has been experiencing a series of E coli outbreaks in products ranging from onions to, most recently, ground beef.

More than 167,000 pounds (75.75 tonnes) of ground beef have been recalled after people fell sick from eating hamburgers at restaurants with a common meat supplier.

Here’s what to know about the current outbreak and the bacteria.

What is E coli and is it dangerous?

Escherichia coli, commonly shortened to E coli, is a bacterium found in the environment, intestines of people and animals, and food. While most strains are harmless, some, like E coli O157:H7, can cause serious illness, and even death.

This strain produces toxins that can lead to severe gastrointestinal symptoms and complications, including damage to the blood vessels in the kidneys. Children, the elderly and immunocompromised individuals are especially vulnerable to E coli.

What do we know about the recent infections and casualties?

Between November 2 and November 14, at least 19 people in Minnesota fell ill from eating meat contaminated with E coli. This led to a national recall of nearly 76 tonnes of ground beef by Detroit-based Wolverine Packing Co.

The contaminated meat, distributed to restaurants nationwide, was traced to hamburgers served at Red Cow and Hen House Eatery locations in Minnesota. No cases have been reported outside the state, and the investigation is ongoing.

Four individuals were hospitalised, including two people who developed serious kidney complications.

“The problem was discovered when FSIS was notified by the Minnesota Department of Agriculture of a group of ill persons who had reported that they consumed ground beef prior to their illness,” said the US Department of Agriculture’s Food Safety and Inspection Service (FSIS).

In late October, in a separate outbreak, chopped onions from California-based Taylor Farms, which are used in McDonald’s Quarter Pounders, were confirmed by the US Food and Drug Administration to be the source of an E coli infection.

At least 104 people across 14 states fell sick. Thirty-four of them were hospitalised, four developed potentially life-threatening kidney disease, and one person died in Colorado.

Colorado’s Department of Agriculture ruled out beef patties as the cause of that outbreak. McDonald’s also temporarily removed Quarter Pounders in a fifth of its 14,000 restaurants in the US as a precaution.

How does E coli contaminate meat and produce?

E coli can contaminate meat during animal slaughtering and processing. The bacteria, which are naturally present in the intestines of healthy cattle, can spread to the meat if intestinal contents or faecal matter comes into contact with the carcass. This risk increases during improper handling or insufficient sanitation in slaughterhouses.

Ground beef is especially susceptible because it combines meat from multiple animals, increasing the likelihood of contamination.

For produce, contamination occurs when vegetables come into contact with water or soil carrying E coli during harvesting, processing, or handling.

For example, run-off water that flows across livestock farms, often after rain, can carry pollutants like animal waste into irrigation systems or other water sources, such as rivers, potentially spreading bacteria like E coli to crops.

How does E coli in food infect humans?

After food contaminated with E coli is consumed, bacteria enter the digestive system and attach to the lining of the intestines.

Strains like E coli O157:H7 release toxins that damage the intestinal walls and cause symptoms such as abdominal cramps.

Humans can also get E coli from drinking or swimming in contaminated water, direct contact with an infected person, handling infected animals or meat, touching contaminated surfaces, or consuming unpasteurised milk and juices.

Pasteurisation involves heating food or liquids to a specific temperature to kill harmful bacteria while preserving product quality.

When proper hygiene and food safety measures, such as handwashing and cleaning surfaces, are not practised, the risk of infection increases.

Does cooking kill E coli in food?

Yes, E coli can be killed by cooking food at a temperature of at least 71 degrees Celsius (160 degrees Fahrenheit).

Raw produce, when not handled or cleaned properly, is at risk for contamination. Safe handling involves:

• Rinsing fruits and vegetables to wash away surface bacteria that may come from soil or water. Meat should not be rinsed — it can carry higher amounts of harmful bacteria, which can splash onto nearby surfaces and food
• Discarding the outer leaves of leafy vegetables like lettuce or cabbage, which are more likely to carry contaminants
• Ensuring knives, cutting boards and countertops are sanitised to avoid cross-contamination
• Storing produce and meat at the recommended temperature

What are the first signs of an infection?

Symptoms of an infection typically appear three to four days after exposure, but it can take up to nine days.

Early signs include:

• Diarrhoea, often bloody
• Stomach cramps
• Fever over 102°F (38.9°C)
• Vomiting
• In severe cases, symptoms like reduced urination and extreme fatigue may indicate kidney complications.

How are E coli infections treated?

Most infections resolve on their own within five to seven days.

Treatment typically focuses on hydration to counter diarrhoea-induced dehydration.

Antibiotics are generally avoided as they may worsen symptoms. This is because antibiotics can cause E coli to release harmful toxins, which can intensify symptoms and damage blood vessels.

Antibiotics can also disrupt the balance of good bacteria in the gut, potentially slowing recovery.

Severe cases of infection, especially those involving kidney vessel damage, may require hospitalisation and kidney dialysis.

What’s next?

The FSIS said it was “concerned that some product may be in restaurant refrigerators or freezers”. It advised restaurants to discard meat products with a “used by” date of November 14, 2024, and frozen products with production dates of October 22, 2024.

Overall, 167,277 pounds (75.875 tonnes) of ground beef have been recalled.

Wolverine Packing Co told the New York Post that it is “conducting an intensive internal audit to fully review suppliers and processes in place, including rigorous quality control measures”.

In the case of the McDonald’s outbreak, two people have filed lawsuits, each seeking a minimum of $50,000 in damages.

Earlier in November, McDonald’s also said it is investing $100m to bring customers back to stores after the outbreak, including $65m that will go directly to the hardest-hit franchises.