E. coli is a type of bacteria that normally lives in the intestines of people and animals. Although most strains of E. coli are harmless, some can cause illness. The strain O157:H7 produces a powerful toxin and can cause severe food poisoning. Understanding how this bacteria works and spreads can help prevent outbreaks.
What is E. coli O157:H7?
E. coli O157:H7 is a specific strain of Escherichia coli bacteria. It produces a powerful toxin called Shiga toxin that attacks the lining of the intestine. Infection with this strain can cause severe stomach cramps, bloody diarrhea, and vomiting. In some cases, it leads to a life-threatening complication called hemolytic uremic syndrome (HUS), which causes kidney failure.
E. coli O157:H7 is classified as an enterohemorrhagic E. coli (EHEC). Other strains that produce Shiga toxin are also referred to as Shiga toxin-producing E. coli (STEC). About 200 O serogroups of E. coli have been identified, but O157:H7 is the serotype most commonly associated with foodborne outbreaks.
How does E. coli O157:H7 spread?
E. coli O157:H7 lives in the intestines of cattle and other ruminants. The bacteria does not make the animals sick. The animals shed the bacteria in their feces, which can then contaminate food or water sources.
Humans can become infected by:
- Eating contaminated foods – Especially undercooked ground beef, raw milk, unpasteurized juice and cheeses made from raw milk. Fruits and vegetables can also harbor E. coli if contaminated by feces.
- Drinking contaminated water – Water can become contaminated if feces enters the water supply.
- Contact with contaminated people or animals – The bacteria can spread person-to-person, especially among children in daycares. It can also spread by petting animals or visiting farms.
Infected people continue shedding the bacteria in their feces for about a week after symptoms end. Good hygiene like handwashing helps prevent spread.
What foods are associated with E. coli O157:H7?
| Food | Risk Factors |
|---|---|
| Raw or undercooked ground beef | E. coli originates from cow intestines and can contaminate meat during slaughter. Grinding mixes bacteria throughout the meat. |
| Raw milk and unpasteurized cheeses | Cow feces can contaminate milk. Pasteurization kills E. coli. |
| Unpasteurized juice | Bacteria from animal feces can contaminate fruit used to make juices. |
| Raw fruits and vegetables | Irrigation with contaminated water or contact with feces from animals can spread E. coli. |
Other risky foods include salami, deli meats, sprouts, and lettuce. Insufficient cooking, cross-contamination, and poor hygiene practices contribute to outbreaks.
What are the symptoms of an E. coli O157:H7 infection?
Symptoms of E. coli O157:H7 infection include:
- Severe stomach cramps
- Diarrhea – often bloody
- Vomiting
- Low fever
Symptoms typically start 3-4 days after ingesting the bacteria, but may appear anywhere from 1-10 days after exposure. Most people recover without antibiotics in 5-10 days.
In some cases, the infection causes hemolytic uremic syndrome (HUS), which is a medical emergency. Symptoms of HUS include little or no urine output, drowsiness, pallor, and easy bruising. HUS causes kidney failure and occurs in around 5-10% of E. coli O157:H7 infections, mostly in children under 5.
How is E. coli O157:H7 infection diagnosed?
Doctors suspect E. coli O157:H7 if a patient has symptoms of bloody diarrhea. Diagnostic tests may include:
- Stool culture – A sample of stool is analyzed in a lab for presence of the bacteria.
- Polymerase chain reaction (PCR) – A molecular test that can identify Shiga toxin and specific genes of E. coli O157:H7 in a stool sample.
- Blood tests – May show anemia and elevated levels of white blood cells, which are signs of an infection.
Identifying the specific strain of E. coli helps distinguish typical E. coli infections from the more virulent E. coli O157:H7.
How is E. coli O157:H7 infection treated?
Treatment focuses on maintaining hydration and controlling symptoms while the infection runs its course.
- Oral rehydration solutions can help prevent dehydration. Hospitalization for IV fluids may be necessary for children or severe dehydration.
- Antidiarrheal medications are usually avoided as they may increase the risk of HUS. Doctors may use antibiotics judiciously in some severe cases.
- Patients with HUS may require dialysis, blood transfusions, and intensive care.
Most people recover without antibiotics, since these bacteria do not respond to common antibiotics used to treat other E. coli infections. However, antibiotics may be used in some severe cases under medical supervision.
How can E. coli O157:H7 be prevented?
Preventing E. coli O157:H7 outbreaks requires action across the food supply chain from farm to table.
On the farm
- Keep cows’ feed and water free of contamination from feces
- Promote good sanitation practices when milking cows
- Separate sick animals from the herd
- Use manure as fertilizer at least 4 months before harvesting produce
During meat processing
- Prevent cross-contamination in slaughter facilities through proper carcass handling
- Follow procedures to minimize feces contact during slaughter and processing
- Use antimicrobial rinses on carcasses
- Monitor cleanliness of equipment and food contact surfaces
During food production and sale
- Pasteurize milk, juice, and other products
- Follow guidelines for washing fruits and vegetables
- Cook ground beef thoroughly to 160°F
- Prevent cross-contamination between raw meats and produce
- Maintain proper temperatures in storage and transport
- Practice good personal hygiene when handling food
In food service and home kitchens
- Wash hands thoroughly with soap before and after handling food
- Sanitize countertops and utensils after contact with raw meat
- Separate raw and cooked foods
- Cook meats like ground beef to recommended safe internal temperatures
- Wash all produce thoroughly
- Drink only pasteurized milk and juices
Following science-based prevention practices at every step reduces opportunities for E. coli contamination. Proper cooking kills the bacteria, but contamination can still occur if raw meats cross-contaminate other foods or surfaces. Vigilant handwashing protects both food handlers and consumers.
Conclusion
E. coli O157:H7 is a dangerous strain of bacteria that can cause severe illness, especially in children. Preventing E. coli infections requires diligence from farm to table. Washing hands before and after handling food offers a simple but effective protection against E. coli and many other harmful germs. Cook meats thoroughly and separate raw and cooked foods to avoid cross-contamination. Following basic food safety guidelines minimizes opportunities for E. coli to spread through the food supply. With proactive prevention measures in place across the system, we can outsmart E. coli and protect public health.