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19.11.2020 - Foods

What are STEC, VTEC, and EHEC? An overview and their significance in food

Certain toxin-producing strains of E. coli can cause diarrhea and more severe illnesses in humans, such as the hemolytic-uremic syndrome (HUS). Kidney failure and even death can result from this condition. In this article, we answer your questions about STEC, VTEC, and EHEC.

What are EHEC?

EHEC stands for enterohemorrhagic Escherichia coli. These bacteria have the ability to form strong cell toxins, known as Shiga and Vero toxins, and are summarized as STEC/VTEC (Shiga or Vero toxin-producing Escherichia coli). The terms STEC and VTEC are used synonymously.

Not all STEC/VTEC cause illnesses in humans. Only those STEC/VTEC capable of causing severe illnesses in humans are referred to as EHEC.

There are two types of Shiga toxins: stx1 and stx2. Other pathogenicity factors of EHEC include the ability to adhere to intestinal cells (eae gene: formation of the intimin protein) and the formation of the protein enterohemolysin (ehly gene). Severe illnesses are almost exclusively caused by stx2-positive EHEC strains.

Based on their antigen structure, EHEC are classified into different serogroups or serovars according to O and H antigens. The best-known representative is O157:H7. Other commonly represented serogroups are O26, O45, O103, O104:H4, O111, O121, and O145.

O104:H4 caused the largest EHEC outbreak in Germany to date, which was linked to fenugreek sprouts, resulting in approximately 4000 cases and 53 deaths.

Due to the reasons of preventive consumer protection and because it’s not yet conclusively known which properties make an STEC/VTEC an EHEC, all STEC/VTEC are still considered as potential EHEC.

Occurrence and transmission routes:

Escherichia coli bacteria are part of the normal intestinal flora of humans and

animals. Detecting E. coli serves as an indicator of fecal contamination. The intestines of ruminants such as cattle, sheep, and goats, as well as deer, are the natural reservoir of enterohemorrhagic Escherichia coli (EHEC) and are shed through feces. The bacteria can enter foods during slaughtering or milking, for example. EHEC is mainly detected in raw or insufficiently heated foods like raw milk, raw milk cheese, raw or undercooked meat, minced meat from ruminants, or spreadable raw sausages (e.g., mett).

Contaminated water or cattle manure can also contaminate raw fruits and vegetables grown on or near the ground with EHEC (e.g., unpasteurized apple juice, raw leafy vegetables like sprouts, spinach, salad, ...).

Transmission through cross-contamination from contaminated, mostly raw foods to another, mostly ready-to-eat food or indirect transmission via hands, devices, work surfaces, knives, etc., is also possible.

Furthermore, alongside foodborne transmissions, human-to-human transmissions or direct contact with animals (e.g., petting zoo) are significant transmission routes. These routes are possible due to a very low infectious dose of <100 CFU (CFU = colony-forming units) (for O157:H7).

Incubation period, symptoms, and risk groups:

The incubation period, i.e., the time between infection and the emergence of initial symptoms, is 2-10 days, with an average of about 3-4 days (based on studies on EHEC serogroup O157). Symptoms range from mild gastrointestinal complaints with diarrhea to severe bloody diarrhea, often accompanied by abdominal cramps, nausea, vomiting, and fever (hemorrhagic colitis (HC)). Five to 12 days, usually around seven days after diarrhea onset, HUS diseases associated with EHEC (HUS: hemolytic-uremic syndrome) can occur. HUS causes damage to blood vessels, red blood cells, and the kidneys, often requiring dialysis. Neurological damage and other organ complications such as pancreatic and heart damage can occur due to HUS.

Children under 5 years old, the elderly, and immunocompromised individuals are particularly often affected by severe EHEC infections with bloody diarrhea and HUS.

Preventive hygiene measures:

• EHEC is killed by heat treatments such as cooking, roasting, and pasteurization. This requires that perishable foods and dishes reach a core temperature of ≥70°C for at least 2 minutes. EHEC is relatively insensitive to acidic pH, cold, drying, and high salt concentration. Even deep freezing does not reliably kill EHEC.
• Boil raw milk before consumption.
• Raw animal-derived foods and perishable foods should be stored at refrigerator temperature.
• To avoid cross-contamination, meat and other raw foods should not be prepared simultaneously with other ready-to-eat foods and should, under no circumstances, be prepared using the same utensils and surfaces.
• Hands should be washed thoroughly before preparing meals and after handling raw meat.
• After contact with raw meat, clean and dry surfaces and objects thoroughly, replace cloths and towels, and wash them at at least 60°C.

Reporting obligation according to the Infection Protection Act (IfSG):

According to § 6 para. 1 no. 1 letter f) IfSG, suspicion of the disease, illness, and death from hemolytic-uremic syndrome (HUS), and according to § 7 para. 1 no. 13 IfSG, direct or indirect evidence of EHEC, insofar as it indicates an acute infection, must be reported by name to the public health office. The report must be submitted within 24 hours of becoming aware. § 8 IfSG names the individuals obligated to report (e.g., doctor, pathologist, veterinarian), and § 9 outlines the information that must be included in the report.

Investigation steps in our laboratory:

1. Enrichment
2. Realtime (RT)-PCR
3. Cultural confirmation upon a positive finding (in consultation)
4. If required: Serotyping (O26, O45, O103, O104, O111, O121, O145, O157)

More information on Escherichia coli and STEC/VTEC can be found in our BAV fact sheets:

1. What is the significance of Escherichia coli in food  
2. What is EHEC/ STEC/ VTEC 

In our laboratory, we regularly conduct investigations on Escherichia coli, STEC/VTEC, and other pathogenic microorganisms. We provide fast and reliable results. Our customer service representatives are available to answer your queries.

Sources: 

Federal Institute for Risk Assessment (BfR) –  following link, as well as here

Robert Koch Institute (RKI) - following link

Bavarian State Office for Health and Food Safety (LGL Bayern) -  following link 

Lower Saxony State Office for Consumer Protection and Food Safety (Laves) -  following link