Shiga toxin-producing 𝙀𝙨𝙘𝙝𝙚𝙧𝙞𝙘𝙝𝙞𝙖 𝙘𝙤𝙡𝙞

STEC infection in humans can occur ( WHO factsheet on E. coli, 2018 ):

• As an asymptomatic infection (“carriers”)
• As a gastrointestinal disease, which can manifest in different forms, from moderate to even severe particularly in certain populations.

The symptomatic forms of the disease are more often observed in:

• Young children, particularly those under 3 years of age
• Elderly individuals
• Pregnant women
• Immuno-compromised people

When symptoms occur, they usually appear after an incubation period of 3 to 4 days from exposure (range: 2 to 12 days). The gastrointestinal system is mainly affected ( CDC, About Escherichia coli Infection, 2024 ), with:

• Abdominal cramps
• Diarrhoea (from mild to bloody)
• Vomiting and nausea
• Fever in some cases, usually not exceeding 38.5°C

In most cases, the infection resolves within 5 to 7 days. However, life-threatening complications can sometimes develop ( Bruyand et al., 2018 ), including:

• Haemorrhagic colitis
• Intestinal stenosis/perforation/necrosis, requiring urgent surgery
• Pancreatitis
• Diabetes
• Central nervous system involvement, leading to torpor, mental disturbance, diplopia, seizures, and coma

Additionally, around 10% of symptomatic human STEC cases, mostly in children, the elderly, and immunocompromised individuals, may develop haemolytic uraemic syndrome (HUS), a severe condition characterised by haemolytic anaemia, thrombocytopenia, and acute renal injury ( Bruyand et al., 2018 ).

Symptoms associated with HUS may include:

• Fatigue
• Dizziness
• Shortness of breath
• Pallor
• Petechiae, bruising, and oedema in some patients

HUS is a serious condition that can be fatal in 3–5% of cases ( WHO factsheet on E. coli, 2018 ). During the acute phase, more than half of patients need dialysis, and most require red blood cells transfusion ( Bruyand et al., 2018 ).

According to the World Health Organisation's report on the global burden of foodborne diseases ( WHO, 2015 ), foodborne STEC was responsible for over 1.2 million illnesses, 128 deaths, and nearly 13,000 disability adjusted life years (DALYs) in 2010, worldwide.

Despite its  pathogenicity  for humans, STEC infection in animals is generally asymptomatic ( WOAH Terrestrial Manual, 2018 ). However, STEC producing Stx2e are an important cause of oedema disease in pigs ( Yoshimura et al., 2023 ) and certain STEC types can cause diarrhoea in young calves or swine ( Barros M.M. et al., 2023 ;  Khawaskar et al., 2022 ).

In animals, the main risk factors for infection with STEC are age, weaning, animal movements, season, feed composition, and the bacteria's ability to persist in the environment ( Fairbrother and Nadeau, 2006 ). The presence of STEC in the animal gut could be controlled through strategies such as vaccination, administration of  bacteriophages , changes in nutrition and administration of probiotics.

STEC lives in the gut of ruminants that can spread the bacteria with their droppings. The main animal species responsible for human infection are ( CDC, 2019 ):

• Cattle (especially calves)
• Sheep
• Goats
• Deer

STEC has been sporadically isolated from other animals that can be transient carriers, such as ( ISS STEC, 2023 ):

• Water buffalo
• Pigs
• Horses
• Dogs
• Farmed rabbits

Infected animal faeces can contaminate the farm environment (e.g., manure, ponds, lakes, dams and wells, barns, calf hutches, straw and other bedding, feed and feed troughs, water and water troughs and farm equipment) and the surrounding ground, pastures and watercourses ( Bach et al., 2002 ).  

Therefore, STEC can be found in:

• Feed
• Water
• Soil
• Plants
• Food intended for human consumption (if hygiene measures are ineffective)

Sources of STEC are:

• Contaminated meat (mostly beef), due to poor processing methods during slaughter
• Milk contaminated during milking when hygiene rules are not followed, and cheese produced with such milk
• Vegetables, fruits, sprouts, and seeds fertilised and irrigated with contaminated manure and water
• Private well water contaminated by faeces and not subjected to chlorination
• Food contaminated directly by individuals preparing meals who do not follow proper hygiene measures

For information on the source of STEC, please see the annual  EU One Health Zoonoses report  ( ANSES data sheet, 2011 ;  CDC Foods That Can Cause Food Poisoning, 2022 ;  ECDC STEC infection, 2020 ;  FAO and WHO, 2018 ).

Shiga toxin-producing Escherichia coli (STEC) may spread to humans, directly and indirectly, through the following routes of transmission:

• Consumption (or handling) of contaminated food or water (foodborne and waterborne infection)
• Contact with infected animals and/or their excrements
• Contact with a contaminated environment (e.g., recreational waters)
• Person-to-person contact (faecal-oral inter-human transmission)

STEC can be found in a variety of food categories of both animal and non-animal origin:

• Meat, mainly beef
• Milk, cheese and other dairy products
• Processed foods (e.g., bakery products)
• Fruits, vegetables, seeds and sprouts

Raw and undercooked foods are the primary sources of STEC infection in humans, also because of possible cross-contamination during food preparation. In leafy vegetables, such as lettuce and spinach, STEC may penetrate and persist in plant tissues. Ready-to-eat (RTE) foods also pose a significant risk to consumers. The presence of STEC in bakery products has been reported in the EU, with flour as the probable source of contamination ( EU One Health 2021 Zoonoses Report ).

Seeds and sprouts (such as alfalfa, bean, or any other sprout or seed species) are considered a risk for food poisoning with STEC: the environmental conditions necessary for sprouts to be produced are suitable for growth of bacteria, and contamination may occur in seeds used for sprout production, long before the consumption ( CDC Foods That Can Cause Food Poisoning, 2022 ;  Soon et al., 2013 ).

Contaminated water can be responsible for indirect transmission of STEC, especially when used for irrigation, leading to contamination of vegetables, for example. Water can also directly cause STEC infections, for example in people swimming in contaminated freshwater lakes and pools ( CDC, About Escherichia coli Infection, 2024 ;  WHO factsheet on E. coli, 2018 ).

The number of bacteria needed to cause the disease in humans may be very low ( ANSES data sheet, 2011 ). The probability of developing the disease after exposure depends on the number of STEC cells ingested, and on the type of food consumed, which may protect STEC during passage through the gastrointestinal tract ( EFSA BIOHAZ Panel et al., 2020 ).

Animals can become infected through:

• Direct contact with faeces of infected animals
• Indirect contact with contaminated water and feed

STEC can persist in stables through faecal contamination of forage, especially when ensiling or conservation methods are inadequate.

• STEC infection was the third most commonly reported gastrointestinal foodborne illness in humans in the European Union.
• In 2023, there were 10,217 confirmed cases of human STEC infections, corresponding to a European Union notification rate of 3.1 cases per 100,000 population. This was an increase of 30.0% compared with 2022 (2.4 cases per 100,000 population).
• The overall trend for STEC infections showed an increase in the 2019–2023 period.
• In 2023, a total of 505 HUS cases were reported from 20 Member States.
• In 2023, STEC were isolated from 354 food sampling units of the 16,117 units sampled with ‘objective sampling’ as sampling strategy and tested with methods detecting any STEC. The ‘ready-to-eat’ food category included 6863 sampling units reported by 19 Member States and 1.0% were positive for STEC, with positive sampling units originating mainly from the ‘milk and milk products’ (2.0% positives) and ‘meat and meat products’ (1.3%) food categories. However, 6.7% of the 45 sampling units belonging to the ‘bakery products’ food category were also positive for the presence of STEC. Out of the 9254 ‘non-ready-to-eat’ samples reported by 21 Member States, 3.1% were positive, with the highest level of contamination in ‘meat and meat products’ (3.8%).
• Nine Member States tested 536 official control samples of ‘sprouted seeds’ in the context of  Commission Regulation (EC) No 2073/2005  taken at retail and processing plants, with no positive results.
• In 2023, STEC testing was carried out by five Member States on animal samples belonging to different categories. Most of the units tested in the European Union (N=2129) were from ‘cattle’ (N=937), with 16.8% positives. The highest proportions of positive samples were obtained from the following animal categories: ‘pigs’ with 46.9%, ‘goats and sheep’ with 34.6%, based on 408 and 405 animal samples tested, respectively. 

For more information on Shiga toxin-producing Escherichia coli reported in humans, animals and food in the EU and other reporting countries in 2023 and in previous years, refer to the  2023 EU One Health Zoonoses Report , to the online  dashboard on Shiga toxin-producing Escherichia coli , and to the online  dashboard on foodborne outbreaks  published by EFSA.

The prevention of STEC infection relies on a comprehensive "farm to fork" approach.

• Applying good farming practices, including hygiene in handling, managing and storage of feed, bedding, farm environment e.g., handwashing after direct contact with animals (particularly calves) or their environment.
• Implementing good agricultural practices, such as manure management, irrigation practices.
• Protecting freshwater sources and untreated drinking water supplies from contamination by animal manure.
• Ensuring good hygiene practices during milking to avoid faecal contamination of milk.
• Immunising cattle to reduce the prevalence of STEC.
• Organising continuous biosecurity training for farm managers and farm workers.

• Verifying compliance with microbiological  food safety criterion  (FSC) by food business operators, through own-checks according to the hazard analysis critical control points ( HACCP ) programmes.
• Ensuring regular and proper official controls by competent authorities.
• Implementing FSC by food business operators and verified by the competent authority ( Regulation (EC) No. 2073/200 5).
• Applying good hygiene practices for meat production, e.g., avoiding faecal contamination of meat during animal slaughter.
• Applying approved bactericidal treatment to foods such as heating or irradiation.
• Offering continuous food safety training for food business operators.
• Ensuring strict personal hygiene to prevent contact between food and infected food handlers.
• Promoting constant maintenance of the cold chain during the handling, transport and storage of food items.

• Implementing FSC by food business operators and verification by the competent authority ( Regulation (EC) No. 2073/2005 ).
• Promoting constant maintenance of the cold chain during handling, transport and storage of food items.
• Ensuring regular and proper official controls by competent authorities.

• Handling and preparing food in a proper way (i.e., do not leaving food out of the refrigerator for a long period of time, or not adequately cleaning utensils or surfaces).
• Avoiding cross-contamination between raw and ready-to-eat products.
• Washing properly and, if not possible, peel or cook vegetables and fruits.
• Avoiding the consumption of raw milk and products thereof from uncontrolled producers.
• Avoiding swallowing water while swimming in lakes, ponds, streams, and pools with untreated (not sanitised) water.

 Before preparing, serving or eating food, carefully washing hands, especially in case of:

• Using the toilet or changing nappies (diapers)
• Being in contact with animals or their environment (e.g., farms, petting zoos or fairs)
• Being in contact with faeces from household pets
• Handling raw vegetables, fruit, or meat

The “ Five Keys to Safer Food ” were developed by WHO to educate consumers and food handlers on the safe handling of food.

 _{Click on the plus sign in the right-hand panel for more information on each element.}  

Data on STEC are collected across the entire food chain.

Surveillance in humans

•  Commission Implementing Decision (EU) 2018/945  provides case definitions for a range of communicable diseases, including STEC cases.
•  Regulation (EU) 2022/2371  establishes rules on relevant cross-border threats to health, including epidemiological surveillance, monitoring, early warning, and response actions.
• ECDC collects, analyses and disseminates data on human cases ( ECDC’s Surveillance Atlas of Infectious Diseases ) in compliance with Regulation (EU) 2022/2371 and uses indicator-based surveillance data to produce its  Annual Epidemiological Reports .

Surveillance in food and feed

•  Regulation (EC) No. 2073/2005  establishes a STEC food safety criterion for sprouts at the retail level. In sprouts placed on the market during the shelf life, the safety criterion requires the “absence in 25 grams” of STEC O157, O26, O111, O103, O145, and O104:H4.
• Food business operators must verify compliance with the microbiological criterion, through own-checks according to their HACCP programme.
• STEC monitoring data on food are collected and reported by Member States in compliance with the Zoonoses  Directive 2003/99/EC , covering sampling results from both official controls and food business operators (industry sampling, HACCP and own-checks).
• Institutional and own-check controls on food are implemented in the event of an outbreak investigation.
• No harmonised surveillance programmes for STEC in feed and food have been established in the EU.

Surveillance in animals

• STEC monitoring data from animals are collected and reported in compliance with the Zoonoses Directive 2003/99/EC.
• No harmonised surveillance programmes for STEC in animals have been established in the EU.

 Surveillance of antimicrobial resistance

• There is no surveillance of ad hoc antimicrobial resistance for STEC in the EU.

An important component of food safety is safeguarding the health of animals: food safety begins at the farm with the prevention of animal diseases. To protect consumers from this threat, the EU has adopted an integrated approach to food safety from farm to fork, involving all key players: EU Member States, the European Commission, the European Parliament, EFSA, ECDC and the European Union Reference Laboratories.

Data on the occurrence of STEC in animals and food, in humans are collected by EFSA and ECDC, respectively, and analysed in the annual  EU One Health Zoonoses report  prepared by EFSA and ECDC.

In particular, EFSA has a crucial role in:

• Supplying independent scientific advice and assistance on food safety aspects relating to STEC through EFSA’s Panel on Biological Hazards, concerning food safety and food-borne diseases
• Supporting European and national risk managers in monitoring and evaluating the prevalence of STEC in animals and foods, and suggesting control measures when needed
•  Preparedness and response (EFSA)  in the event of food or feed safety incidents or crisis. In case of multi-country foodborne outbreaks, EFSA and ECDC are responsible for the rapid outbreak assessment.

EFSA is assisted by its network on zoonoses monitoring data, a pan-European network of national representatives and international organisations that support EFSA by gathering and sharing information on zoonoses in their respective countries.

The European Union Reference Laboratories (EURLs)

The European Union Reference Laboratories (EURLs) are appointed by the European Commission and aim to ensure high-quality methods of analysis, as well as uniform testing and diagnosis within the areas of animal health and food microbiology in the EU. EURLs also aim to coordinate the activities of national reference laboratories and provide necessary support to EFSA in monitoring zoonoses (guidance for reporting, advice, etc).

The EURL for STEC is hosted by the Italian National Health Institute,  Istituto Superiore di Sanità (ISS) .