Toxin-producing E. coli infections

Shigatoxin-producing Escherichia coli bacteria (STEC, also known as verocytotoxin-producing E. coli (VTEC) or enterohemorrhagic E. coli (EHEC)), are a group of zoonotic pathogens (i.e., originating from animals) that cause diarrhoea or more severe diseases after the ingestion of contaminated food or water, or after contact with infected animals (Vanaja et al., 2013). In Europe, STEC is among the four most common causes of food-borne diseases, next to campylobacteriosis and salmonellosis (ECDC, 2021). More frequent heavy rainfall events and increased temperature in the future create optimal conditions for bacterial growth, survival and spreading, and increase the STEC-related infection risk.

Source & transmission

E. coli bacteria are present in healthy intestines of humans and animals (including cattle, sheep, goats, as well as deer and elk). Yet, STEC pose risks of food contamination when animal faeces are not handled sanitary. Already at relatively low numbers, STEC can cause disease symptoms (Pacheco and Sperandio, 2012).

STEC infections, like other infections with E. coli bacteria, are often acquired during milking or slaughtering, especially when handling cattle, or for children in petting zoos. Besides infections via direct contact, food-borne transmission is common since the bacteria can be present in raw or insufficiently heated food products, such as raw milk and cheese, and raw or undercooked meat. Also raw fruits and vegetables can be contaminated with STEC, after contact with cattle faeces or contaminated water or soil. Indirectly, contact with contaminated hands, utensils, kitchen work surfaces or knives, and cross-contamination in ready-to-eat food are also possible routes for infection. In addition, human-to-human contact can also cause infections, even with very low bacterial presence (WHO, 2022; CDC, 2022).

Health effects

STEC symptoms usually arise between 2 to 10 days after ingestion of the bacteria and cause mostly gastrointestinal problems ranging from mild to severe bloody diarrhoea, which is often associated with abdominal cramps, nausea, vomiting, fever or haemorrhagic colitis (HC). HC causes severe bloody diarrhoea several days after the onset of initial symptoms (Cohen and Gianella, 1992), and also the haemolytic uremic syndrome (HUS) may then occur. In 5 to 7% of STEC infections, the patient suffers from HUS, which is especially risky for young children, the elderly or people with a low immunity who may develop severe complications (Pacheco and Sperandio, 2012). In these cases, blood vessels, red blood cells and kidneys may be damaged, which can further permanently damage the nervous system and other organs such as the pancreas and heart (Pacheco and Sperandio, 2012).

Morbidity & mortality

In the EEA member countries (excluding Switzerland and Türkiye due to absence of data), in the period 2007-2021:

71,539 infections, and an overall notification rate of 2.2 cases per 100 000 population in 2021
Moderate probability of hospitalisation (30-40% of all cases with a known hospitalisation status)
186 deaths were reported, and a mortality rate of about 0.25%. However, for infections that progress to HUS, the mortality rate rises up to 0.6-5%
Increasing incidence trend since 2007, possibly partly due to increased awareness and altered diagnostics. In 2020 the number of reported cases dropped was lower, probably due to the Covid-19 pandemic and possible underreporting.
Most STEC cases were sporadic, but outbreaks occured every year. In the spring of 2011, an aggressive STEC strain caused two outbreaks in Europe, affecting about 4 000 people in 16 countries, with Germany reporting the highest case numbers. The outbreak resulted in around 900 cases of HUS and 50 deaths (Foley et al., 2013; Grad et al., 2012).

(ECDC, 2016-2022; ECDC, 2023)

Distribution across population

Age group with the highest disease incidence in Europe: 0 - 4 years old (ECDC, 2016-2022)
Groups at risk of severe infection (including HUS): young children, the elderly and people with low immunity

Climate sensitivity

Climatic Suitability

E. coli bacteria are perfectly adapted to the conditions in animal intestines. They can grow at temperatures between 7 and 50°C, with the optimal temperature at 37°C (WHO, 2022). E. coli bacteria can also survive outside its host, for example, in water or soil at temperatures of as low as 4°C for several days to months (Son and Taylor, 2021). Toxin-producing E. coli strains, like STEC, have a slightly lower survival capacity as the production of toxins requires energy and therefore comes at a fitness cost (van Elsas et al., 2011).

Seasonality

In Europe, more infections occur between June and September (ECDC, 2016-2022).

Climate Change Impact

The increase of extreme weather events could optimize the conditions for bacterial growth, including that of (shigatoxin-producing) E. coli. Heavy rainfalls cause more runoff from agricultural lands, which brings along pathogens from compost and animal faeces and both floods and increased runoff increases the risk of sewer overflow and contamination of surface waters. In addition, low water stands during drought periods elevate pathogen concentrations in the remaining water due to less dilution and lower filtration capacity of the soil. E. coli bacteria are able to adapt well to warmer climates and specifically some STEC strains are very persistent in the environment (van Elsas et al., 2011). Also, higher air temperatures accelerate bacterial growth, for example in unpasteurized milk if not stored properly in at low temperatures. Since raw milk consumption is especially high in Italy, Slovakia, Austria and France, the number of E. coli infections, including those with STEC, is projected to increase due to the warming climate in those countries (Feliciano, 2021). On the contrary, the projected increase in temperatures of cold bathing waters above 4°C will probably decrease E. coli concentrations (Sampson et al., 2006).

Prevention & Treatment

Prevention

Proper food handling before consumption, including (cold) storage, heat treatment and separation to avoid cross-contamination (Uçar et al., 2016)
Efficient sanitary practices in kitchens and for kitchen utensils (Ekici and Dümen, 2019)
Good sanitary hygiene on farms and in slaughterhouses to minimize faecal contamination
Proper faecal disposal and reducing contact with animal manure (Bauza et al., 2020)
Awareness raising about disease transmission
Probiotics, i.e., live and safe Lactobacillus or Bifidobacterium microorganisms (Allocati et al., 2013)

Treatment

No specific treatment
Rehydration and electrolyte replacement
Antimicrobial medication should be avoided to limit the risk of developing HUS
Dialysis (blood replacement), organ-specific therapy and strong pain killers in case of HUS (Bitzan, 2009)

Links to further information

References

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Bitzan, M., 2009, Treatment options for HUS secondary to Escherichia coli O157:H7, Kidney International 75, S62–S66. https://doi.org/10.1038/ki.2008.624

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