Enterohemorrhagic E. coli (EHEC)

What is enterohemorrhagic E. coli?

Escherichia coli (or simply E. coli) is one of the many groups of bacteria that normally live in the intestines of healthy humans and most warm-blooded animals. E. coli bacteria help maintain the balance of normal intestinal bacteria against harmful bacteria.

However, there are hundreds of types or strains of E. coli bacteria. Different strains of E. coli have different characteristics.

One E. coli strain that causes a severe intestinal infection in humans is known as enterohemorrhagic E. coli (EHEC). It’s the most common strain to cause illness in people. It’s different from other E. coli because it produces a potent toxin called Shiga toxin. This toxin damages the lining of the intestinal wall, causing bloody diarrhea.

What causes an EHEC infection?

EHEC is a strain of E. coli that produces a toxin called Shiga toxin. The toxin causes damage to the lining of the intestinal wall. In 1982, EHEC was found as the cause of bloody diarrhea that developed after eating undercooked or raw hamburger meat contaminated with the bacteria. Since that time, outbreaks of EHEC have been linked with other types of foods, such as spinach, lettuce, sprouts, unpasteurized milk, unpasteurized apple juice or apple cider, salami, and well water or surface water areas frequently visited by animals. Outbreaks have also been traced to animals at petting zoos and day care centers.

EHEC is found in the intestines of healthy cattle, goats, deer, and sheep. According to the CDC, the spread of these bacteria to humans may occur in the following manner:

Meat, such as beef from cows, may become contaminated when organisms are accidently mixed in with beef, especially when it is ground. Meat contaminated with EHEC does not smell or taste bad and looks normal. For this reason, it is important to thoroughly cook beef.

Infection may occur after swimming in or drinking water that has been contaminated with EHEC.
The bacteria can also be spread from person-to-person in families and in child care and other institutional care centers.
Who is at risk for an EHEC infection?

Factors that can increase your risk for getting an EHEC infection include:

- Eating undercooked beef
- Drinking raw (unpasteurized) milk
- Drinking contaminated water
- Working with cattle
- Eating food contaminated with animal feces
- Not washing your hands after you use the bathroom

What are the symptoms of an EHEC infection?

An EHEC infection can make you very ill. Symptoms usually begin 2 to 5 days after ingesting contaminated foods or liquids, and may last for up to 8 days or more. The following are some of the most common symptoms associated with EHEC:

- Abdominal cramps
- Severe bloody diarrhea
- Non-bloody diarrhea
- Little to no fever
- Fatigue
- Nausea
- Hemolytic uremic syndrome (HUS), a serious complication that can cause symptoms of decreased urination, extreme fatigue, pale skin, and anemia

How is EHEC diagnosed?

EHEC can be confirmed with a stool culture. Stool samples are tested to compare with the source or contaminated food that has caused an outbreak.

How is EHEC treated?

Antibiotics and antidiarrheal medicines are not used with this type of infection. They may increase the risk of HUS. Recovery for most people with this illness usually occurs within 5 to 10 days. It is important to drink plenty of fluids to prevent dehydration.
If a person develops HUS, hospitalization in an intensive care unit may be required. Treatment may include blood transfusions and kidney dialysis.

What are the complications of an EHEC infection?

If vomiting is moderate to severe, dehydration can occur. Between 5% and 10% of those with an EHEC infection develop hemolytic uremic syndrome. This is a serious complication which may cause the kidneys to stop working due to the destruction of red blood cells and can be life threatening.

Can an EHEC infection be prevented?

CDC recommendations for prevention of the infection include:

- Cook all ground beef, pork, lamb, or sausage thoroughly. Make sure that the cooked meat is gray or brown throughout (not pink), any juices run clear, and the inside is hot.

- Use a digital instant-read meat thermometer to make sure the temperature of the meat has reached a minimum of 160° F.

- If you are served an undercooked hamburger in a restaurant, send it back.

- Wash all vegetables and fruits with water, especially if you do not plan to cook them.

- Use only pasteurized milk and milk products. Avoid raw milk.

- Use only pasteurized juices and ciders.

- Keep raw meat separate from ready-to-eat foods.

- Make sure that infected people, especially children, wash their hands carefully and frequently with soap to reduce the risk of spreading the infection.

- Drink municipal water that has been treated with adequate levels of chlorine, or other effective disinfectants.

- Avoid swallowing lake or pool water while swimming.

- Wash hands thoroughly after using the toilet or changing diapers.

- Wash hands thoroughly after handling animals, animal bedding, or any material contaminated with animal feces.

- People with diarrhea should not: swim in public pools or lakes, bathe with others, or prepare food for others.

References:

Giacometti F, Bonilauri P, Piva S, Scavia G, Amatiste S, Bianchi DM, Losio MN, Bilei S, Cascone G, Comin D, Daminelli P, Decastelli L, Merialdi G, Mioni R, Peli A, Petruzzelli A, Tonucci F, Liuzzo G, Serraino A. Paediatric HUS Cases Related to the Consumption of Raw Milk Sold by Vending Machines in Italy: Quantitative Risk Assessment Based on Escherichia coli O157 Official Controls over 7 years. Zoonoses Public Health. 2017 Nov;64(7):505-516. doi: 10.1111/zph.12331. Epub 2016 Dec 19. PMID: 27991739. [L]

Enterohemorrhagic Escherichia coli, Johns Hopkins Medicine Blog [L]