E. coli O157:H7

Agricultural Disaster Preparedness and Recovery, Food Safety November 18, 2015 Print Friendly and PDF

e coli

E. coli is one of the most common causes of foodborne illness. E. coli, short for Escherichia coli, is a bacterium from the family Enterobacteriaceae usually found in the digestive system of healthy humans and animals. There are hundreds of known E. coli strains, with E. coli O157:H7 and other shiga-toxin producing strains being the most dangerous. This enterohemorrhagic strain (causing bloody diarrhea and colitis) is responsible for an estimated 73,000 cases of infection and 61 deaths in the US annually. E. coli is found everywhere in the environment, but mostly occupies animal surfaces and digestive systems. It is transmitted through fecal contamination, which means foods that may have contacted animals or animal or human wastes should be washed and/or cooked thoroughly before being consumed.

Under a magnification of 6836x, this colorized scanning electron micrograph (SEM) depicted a number of Gram-negative Escherichia coli bacteria of the strain O157:H7. Courtesy of CDC/ National Escherichia, Shigella, Vibrio Reference Unit at CDC.


E. coli O157:H7 is a Gram-negative rod-shaped bacterium that produces potent toxins. These toxins cause severe damage to the intestinal tract lining of those infected with the bacteria. The presence of E. coli O157:H7 toxins is responsible for the symptoms associated with infection: hemorrhagic colitis, hemolytic uremic syndrome (HUS) and even death. The organism can survive at low temperatures and under acidic conditions, making it difficult to eradicate in nature.

Symptoms associated with E. coli O157:H7

An acute disease associated with this organism is named hemorrhagic colitis. The symptoms characteristic of this disease are watery and/or bloody diarrhea, fever, nausea, severe abdominal cramping and vomiting. Because most people recover from this infection on their own, treatment is usually not necessary. Symptoms can appear within hours or up to several days after ingestion of the bacteria (10-100 cells) and the illness duration is normally 5-10 days. Some individuals may develop hemolytic uremic syndrome (HUS). In the very young, this disorder can cause renal failure, hemolytic anemia, permanent loss of kidney function and even death. In the elderly, these symptoms as well as thrombotic thrombocytopenic purpura (HUS with additional neurological dysfunction and/or fever) may occur.

Risk Groups

E. coli O157:H7 can infect anyone but is more prone to attacking the very young (under 5 years) and the very old. This infection is also associated with immuno-compromised patients. Those working in slaughterhouses, farms, hospitals, nursing homes, nursery schools, and food preparation locations have greater exposure than the rest of the population.

Foods commonly associated with E. coli O157:H7

The most common sources of E. coli O157:H7 infections are raw or undercooked hamburger, other meat, game meat, alfalfa sprouts, unpasteurized fruit juices, dry-cured salami, lettuce, cheese curds, unpasteurized or raw milk, contaminated water or ice and person-to-person transmission. Fruits and vegetables can also cause infection due to contact with contaminated water. However, infection is most often due to consumption of undercooked or raw meats. There appears to be a very low infective dose for this organism (10-100 cells), making adequate sanitation and/or proper processing of foods critically important.

Sanitation methods used to prevent infection

The suggestions below are good examples of how to improve and prevent infections www.fmi.org:

In the home

  • Never thaw food on the counter or let it sit out of the refrigerator over two hours.
  • Use refrigerated ground meat in 3-4 days; frozen meat in 3-4 months.
  • Cook meat until the center is gray or brown. Cook to an internal temperature of 160°F (71°C). This should be determined using a meat thermometer that is calibrated regularly.
  • Serve cooked food with clean plates and utensils.
  • Never allow raw foods to contact ready-to-eat foods, utensils and dishes.
  • Drink only pasteurized milk, milk products and fruit juices.
  • Thoroughly wash fruits and vegetables with clean water.
  • Wash hands thoroughly, especially after bathroom use and the handling of diapers.
  • Make sure drinking water is tested and properly treated.

On the farm

  • Check water sources for coliforms routinely.
  • Use only potable water (tested negative for coliforms) for washing fruits and vegetables.
  • Manage fecal waste in a way that fresh water will not become contaminated.

In meat processing facilities

  • Assure GMPs are being used in slaughterhouses and processing units.
  • Use approved carcasses treatments to remove fecal bacteria.

Importance of Hand Washing

Because illness is associated with E. coli O157:H7, handwashing must be thorough. It is important to wash hands before, during and after: handling raw foods, smoking, changing diapers, cleaning, using the restroom and touching soiled equipment or clothing. This is the proper technique for hand washing:

  • Wet hands with warm water.
  • Apply soap and wash hands for 20 seconds.
  • Rinse and dry with a single-use paper towel.
  • Use the paper towel to shut off water faucet and handle doorknob.

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USDA / NIFA

This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.