FAQs Data Reporting Investigation Immunization Resources
Shiga toxin-producing Escherichia coli 0157:H7
Escherichia coli (E. coli) are gram negative bacteria commonly found in the digestive tracts of animals, including humans, where they assist with normal digestive processes. While most E. coli are not associated with disease, some are responsible for causing infections, such as urinary tract infections, as well as gastrointestinal and respiratory illness. Those responsible for causing diarrhea do so through the production of several potent toxins that damage the intestinal lining in various ways. In severe cases, infections can also lead to a life-threatening condition called Hemolytic-Uremic Syndrome (HUS), which involves renal failure and hemolytic anemia. The most common gastrointestinal disease-causing strains are known as Shiga toxin-producing E.coli (STEC), based on their presence of the Shiga-toxin producing verotoxin genes. Of the STEC group most cases and outbreaks historically have involved the serotype O157:H7. However, with the development of better diagnostic tools, other serotypes and pathogenic groups of E. coli are now also becoming increasingly linked to sporadic cases and outbreaks.
E. coli are naturally occurring gastrointestinal bacteria in the stomachs of most mammals, including humans. STEC can also infect and consequently be transmitted in the feces of these animals, with ruminants, such as cattle, deer, elk, goats and sheep being the most common reservoirs. Although less common, other animals can also become infected and act as a source of human infection, including domestic and agricultural species (dogs, cats, pigs, horses, rabbits) and birds (chickens, turkeys).
STEC-associated illness occurs after bacteria are ingested through either the consumption of contaminated food and water or after physical contact with an infected person or animal.
Contaminated food products are the most common source of infection, with contamination occurring at any time during processing.
Foods that have been associated with past outbreaks include:
- Undercooked and raw ground meat or meat products originating from ruminants (cattle, deer, elk, sheep, goats)
- Bacteria in animal intestines can come in contact with and contaminate meat during animal slaughter and processing. The risk of infection is greater with ground meat consumption because the meat can originate from several different animals and any bacteria present are blended throughout the product.
- Other meat products: since other animals can become infected with STEC bacteria, they can also act as a source of infection, including other game meats, pigs and poultry Processed and dry-cured meats, including jerky, salami, summer sausage and pepperoni.
- These meats are also at risk as many are not properly heated and/or become contaminated during processing.
- Processed foods can be contaminated during production, such as raw flour and grains, peanut butter and cookie dough.
- Fresh produce such as alfalfa sprouts, bagged lettuce and leafy greens, raw fruits and vegetables.
- Manure from livestock can contaminate fresh produce through runoff.
- Unpasteurized dairy, such as raw milk and its products (soft cheeses, queso fresco, yogurt).
- Feces from infected ruminants (cattle, sheep or goats) can contaminate raw milk during the milking process allowing STEC bacteria to grow and produce toxins in the absence of unpasteurized juice, such as apple cider and fresh-squeezed juices.
- Bacteria from contaminated produce can survive, grow and produce toxins in the absence of pasteurization which would normally destroy them.
Direct animal contact:
- Harmless as well as disease-causing E. coli can be part of the common intestinal flora of many animals and they can act as a source of gastrointestinal illness for both humans and other animals.
- Infection can occur through contact with an infected animal, their feces and their environment (such as enclosure surfaces).
- Animals linked to past cases of human illness include livestock, domestic pets (especially puppies and kittens) and those associated with petting zoos.
Water sources can also become contaminated with animal (manure from livestock, agricultural runoff or wild animal feces) and human waste and can cause illness when ingested (such as lake water when swimming).
Person-to-person transmission can also occur if thorough hand washing is not practiced after contact with another infected person’s feces, as in the case of caring for an ill individual or changing an infected child’s diaper. Transmission can also take place when an infected individual prepares food for others after not cleaning their hands properly after going to the bathroom.
The incubation period for an STEC infection can range from less than a day to 10 days (average 3-4 days). Symptoms of an STEC infection vary from person to person and may include one or more of the following:
- Diarrhea and/or bloody diarrhea
- Stomach cramps and pain
- If fever is present it can be very mild
- Poor feeding
Severe complications of infection can include symptoms such as hemorrhagic colitis that can progress within 3 weeks after initial symptoms resolve to life-threatening complications such as hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenia purpura (TTP). These severe manifestations occur in about 5-10% of cases and can lead to acute renal failure, hemolytic anemia and thrombocytopenia. Long-term sequelae include permanent kidney damage and neurological complications, as well as death in 3-5% cases.
Early symptoms of HUS include:
- Decreased urination
- Extreme lethargy
- Loss of color in cheeks and lower eyelids.
Those most at risk of developing severe complications and HUS are young children and the elderly, however, healthy older children and young adults can also be affected.
Communicability: shedding of STEC bacteria in stool can last for a week in adults to as long as three weeks in young children. Prolonged carriage and shedding is uncommon.
Sources of Infection and Prevention
General recommendations for avoiding STEC infection include:
Food handling and preparation:
- Cook all meat products to at least 160°C/70°C to destroy any bacteria and/or toxin present
- Always use a thermometer to determine sufficient cooking temperatures are reached, as color is not a reliable indicator of how well the meat is cooked
- Avoid cross-contamination of any raw meat products with other food items, such as fresh produce, during food preparation – do not use the same cutting boards, knives, kitchen utensils etc.
- Keep raw meat products separate from other foods and cooked meat products (do not place cooked hamburgers on the same plate used for raw patties
- Wash all fruits and vegetables prior to consumption, especially if they are to be eaten raw. If possible, peel or cook fruits and vegetables.
- Wash hands, knives, utensils, cutting boards, kitchen surfaces and other materials used when preparing raw food products (including meat, dairy, vegetables and fruit).
- Ensure you refrigerator is at 40°F or lower and freezer 0°F or lower to avoid bacteria from growing.
- Routinely clean the inside walls and shelves of the refrigerator and immediately clean any spills involving high risk foods – use hot soapy water and then rinse.
- Clean up the juices of any raw meat products immediately with hot soapy water and avoid cross-contamination with other foods, especially if they are to be eat uncooked, such as fruits and vegetables.
Vulnerable populations (young children and the elderly) and high risk foods:
- Avoid eating raw or undercooked meat products, especially ground meat (hamburgers).
- Avoid eating any raw dairy products, such as raw or unpasteurized milk and cheese or yogurt made with raw milk (Queso fresco, Queso blanco, Brie, Camembert, Feta).
- Avoid pre-made unpasteurized fruit juices such as ciders and fresh squeezed juices – keep refrigerated at all times if store bought and consume immediately upon juicing.
- Avoid eating store-bought pre-mixed ready to bake products prior to cooking, such as premade store-bought cookie dough.
- Ensure you thoroughly cook or reheat any premade frozen, refrigerated or ready-to-eat meals (such as frozen microwave meals, precooked entrees) to at least 160°C/70°C, prior to consumption.
Thorough hand washing:
- Before you prepare food for yourself or others, or eat a meal.
- After handling any raw, ready-to-eat or processed meat products and any pet foods.
- After contact with any animal, including domestic pets or after visiting or touching an animal enclosure (such as a petting zoo, livestock show or animal cage), even if you didn’t touch an animal directly.
- After using the bathroom, changing diapers or assisting someone with diarrheal symptoms.
- Make sure children always wash their hands before eating, or after using the bathroom or touching an animal or its enclosure.
Recent Texas Trends
Over the last 5 years the average number of cases of illness caused by Shiga-toxin producing E. coli has been around 500 cases per year (ranging from 250-500). The majority of cases or outbreaks where a food source has been identified have involved high risk foods, such as raw or undercooked meat and raw milk. Past large outbreaks involving cases in Texas have been associated with ready-to-eat frozen food products and meals, as well as prepackaged refrigerated cookie dough.