Escherichia coli (E. coli) is a type of bacteria commonly residing in the intestines of humans and warm-blooded animals. While most E. coli strains are harmless, certain types, particularly Shiga toxin-producing E. coli (STEC), pose a significant risk of foodborne illness. Transmission typically occurs through the consumption of contaminated foods like raw or undercooked ground meat, raw milk, and contaminated raw vegetables, including sprouts.
STEC produces Shiga toxins, named for their similarity to toxins produced by Shigella dysenteriae. These bacteria can thrive in temperatures ranging from 7°C to 50°C (44.6°F to 122°F), with an optimal growth temperature of 37°C (98.6°F). Some STEC strains can also survive in acidic environments, down to a pH of 4.4, and in foods with a minimum water activity (aW) of 0.95.
Thoroughly cooking food to a temperature of 70°C (158°F) or higher effectively destroys STEC. E. coli O157:H7 is the most well-known STEC serotype in terms of public health concern. However, other serotypes are also capable of causing sporadic cases and outbreaks.
Recognizing the Symptoms of E. coli Food Poisoning
STEC infections manifest through a range of symptoms, including abdominal cramps and diarrhea. In some instances, the diarrhea can progress to bloody diarrhea, known as hemorrhagic colitis. Fever and vomiting may also accompany the infection. The incubation period typically ranges from 3 to 8 days, with an average of 3 to 4 days. While most individuals recover within 10 days, a small percentage, particularly young children and the elderly, may develop a life-threatening complication called hemolytic uremic syndrome (HUS). HUS is characterized by acute kidney failure, hemolytic anemia, and thrombocytopenia (low blood platelet count).
It is estimated that up to 10% of patients with STEC infection may develop HUS, with a case-fatality rate ranging from 3 to 5%. Overall, HUS is the most common cause of acute renal failure in young children. Approximately 25% of HUS patients experience neurological complications, such as seizures, stroke, and coma. Around 50% of survivors may develop chronic renal sequelae, which are usually mild.
Anyone experiencing bloody diarrhea or severe abdominal cramps should seek medical attention immediately. It’s important to note that antibiotics are generally not recommended for treating STEC infections, as they may potentially increase the risk of developing HUS.
Understanding the Sources and Transmission of E. coli
Most information on STEC focuses on serotype O157:H7 due to its easier biochemical differentiation from other E. coli strains. Cattle are believed to be the primary reservoir for this pathogen. Other ruminants, such as sheep, goats, and deer, are also considered significant reservoirs. While other mammals (pigs, horses, rabbits, dogs, and cats) and birds (chickens and turkeys) have been found to be infected, they are typically less common sources.
E. coli O157:H7 spreads to humans mainly through the consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk. Fecal contamination of water and other foods, as well as cross-contamination during food preparation involving beef, other meat products, contaminated surfaces, and kitchen utensils, can also lead to infection. Some common foods linked to E. coli O157:H7 outbreaks include undercooked hamburgers, dried cured salami, unpasteurized fresh-pressed apple cider, yogurt, and cheese made from raw milk.
Increasingly, outbreaks are traced back to the consumption of contaminated fruits and vegetables (including sprouts, spinach, lettuce, coleslaw, and salad). Contamination can occur through contact with feces from domestic or wild animals during cultivation or handling. STEC has also been found in bodies of water (ponds and streams), wells, and water troughs, and can survive for months in manure and water-trough sediments. Waterborne transmission can occur through contaminated drinking water and recreational waters.
Person-to-person contact is a significant mode of transmission via the oral-fecal route. Asymptomatic carriers, individuals who show no clinical signs of disease but can still infect others, have been reported. The duration of STEC excretion is typically about a week or less in adults but can be longer in children. Visiting farms and other places where the public can directly contact farm animals is also a risk factor for STEC infection.
Effective Prevention Strategies Against E. coli Food Poisoning
Preventing infection requires implementing control measures at all stages of the food chain, from agricultural production on the farm to processing, manufacturing, and food preparation in commercial establishments and household kitchens.
Industry-Level Interventions
The number of disease cases can be reduced by implementing various mitigation strategies for ground beef, such as screening animals pre-slaughter to reduce the introduction of pathogens in the slaughtering environment. Good hygienic slaughtering practices reduce the contamination of carcasses by feces, although these practices do not guarantee the absence of STEC from products.
Educating workers at farms, abattoirs, and those involved in food production about hygienic food handling is essential to minimize microbiological contamination. The only effective method of eliminating STEC from foods is to introduce a bactericidal treatment, such as heating (cooking or pasteurization) or irradiation.
Household Preventive Measures
Preventive measures for E. coli O157:H7 infection are similar to those recommended for other foodborne diseases. Basic good food hygiene practices, as outlined in the WHO’s “Five keys to safer food,” can prevent the transmission of pathogens responsible for many foodborne diseases, including STEC.
The five keys to safer food are:
- Keep clean.
- Separate raw and cooked.
- Cook thoroughly.
- Keep food at safe temperatures.
- Use safe water and raw materials.
These recommendations should be followed diligently, especially the principle of cooking thoroughly, ensuring that the center of the food reaches at least 70°C (158°F). Always wash fruits and vegetables carefully, especially if you intend to eat them raw. If possible, peel vegetables and fruits before consumption. Vulnerable populations, such as small children and the elderly, should avoid consuming raw or undercooked meat products, raw milk, and products made from raw milk.
Regular handwashing, particularly before food preparation or consumption and after toilet use, is highly recommended. This is especially important for those caring for small children, the elderly, or immunocompromised individuals, as the bacterium can spread from person to person, as well as through food, water, and direct contact with animals.
A number of STEC infections have been linked to contact with recreational water. Therefore, protecting these water areas and drinking-water sources from animal waste is crucial.
Best Practices for Fruit and Vegetable Producers
WHO’s “Five keys to growing safer fruits and vegetables” offers rural workers who grow fresh fruits and vegetables for themselves, their families, and for sale in local markets key practices to prevent microbial contamination of fresh produce during planting, growing, harvesting, and storing.
The five keys to growing safer fruits and vegetables are:
- Practice good personal hygiene.
- Protect fields from animal fecal contamination.
- Use treated fecal waste.
- Evaluate and manage risks from irrigation water.
- Keep harvest and storage equipment clean and dry.
WHO’s Role in Combating E. coli Food Poisoning
WHO provides scientific assessments to control STEC in food. These assessments serve as the basis for international food standards, guidelines, and recommendations developed by the Codex Alimentarius Commission.
WHO also promotes the strengthening of food safety systems by promoting good manufacturing practices and educating retailers and consumers about appropriate food handling and avoiding contamination.
During E. coli outbreaks, such as the 2011 outbreak in Europe, WHO supports the coordination of information sharing and collaboration through International Health Regulations and the International Food Safety Authorities Network (INFOSAN) worldwide. WHO works closely with national health authorities and international partners, providing technical assistance and the latest information on outbreaks.
