Research and analysis

Shiga toxin-producing Escherichia coli (STEC) data: 2023

Updated 26 June 2025

Main points for 2023

The main points of the 2023 annual report are:

1. Overall, 2,018 cultured-confirmed cases of Shiga toxin-producing Escherichia coli (STEC) were reported in England during 2023 decrease of 2.2% compared to 2022.
2. A total of 533 culture-confirmed cases of STEC O157 were reported in England in 2023 compared to 762 in 2022, a decrease of 30%. A total of 2,260 cases of STEC non-O157 were reported in England in 2023 (including 1,485 culture-confirmed cases and 755 faecal specimens positive for stx genes on PCR but culture-negative), an increase of 13% compared to 2022 and of 125.6% compared to 2019. Among culture-confirmed non-O157 cases, the most commonly isolated serogroup was STEC O26 (n=256 of 1485, 17.2%).
3. As in 2022, children aged 1 to 4 years had the highest annual incidence of infection due to STEC O157 (4.01 per 100,000 population, 95% confidence interval (CI) 3.27 to 4.88). As in 2022, children aged under 1 years had the highest incidence of infection due to STEC non-O157 (12.74 per 100,000 population, 95% CI 9.98 to 16.01).
4. Where information was available, around a third (28.3%, 140 of 494) of confirmed STEC O157 cases and one third (32.1%, n=233 of 726) of STEC non-O157 cases in England were hospitalised. The proportions of hospitalisations for STEC O157 and STEC non-O157 were similar to the previous year. One death was reported among STEC O157 cases, and 2 deaths among STEC non-O157 cases.
5. Where information was available, 2.1% of STEC O157 cases (11 of 533) and 1.7% (39 of 2,260) of STEC non-O157 reported developing Haemolytic Uraemic Syndrome (HUS). Around 10 percent (n=26) of confirmed STEC O26 cases developed HUS.
6. Seven outbreaks of STEC involving 228 cases, 145 of whom were resident in England, were investigated in 2023. One outbreak involved STEC O157, 3 involved STEC O145, 2 involved STEC O26, and 1 involved STEC O183. A suspected or confirmed vehicle was identified for all 7 outbreaks and included beef, salad leaves, cucumber, dried fruits, and dairy products.

Background

Shiga toxin-producing Escherichia coli (STEC), also known as Vero cytotoxin-producing Escherichia coli (VTEC), are bacteria that can cause gastroenteritis. Symptoms vary from mild to bloody diarrhoea and, in severe cases, can cause haemolytic uraemic syndrome (HUS), a serious and life-threatening condition predominantly affecting the kidneys. A small proportion of patients, mainly children, develop HUS (1).

The main reservoir for STEC is cattle although it is also carried by other ruminants such as sheep, goats and deer. Transmission can occur through direct or indirect contact with animals or their environments, consumption of contaminated food or water, and person to person spread. STEC infections can present as sporadic cases or as outbreaks. Large national and multinational outbreaks have been associated with foodborne transmission (2, 3, 4).

The most common serogroup of STEC notified to UKHSA in England is O157 (5), followed by O26 (6). Some STEC serogroups (termed collectively as non-O157 STEC) can also cause illness and STEC O26, O145 and O103 have been implicated in outbreaks in England, and elsewhere.

Diagnostic laboratories in England use culture methods to detect STEC O157, identified by its inability to ferment sorbitol on selective media (Cefixime-Tellurite Sorbitol MacConkey (CT-SMAC) agar). However, most non-O157 STEC ferment sorbitol and differentiation of non-O157 STEC from faecal commensal E. coli is challenging. Therefore, detection of non-O157 STEC mainly relies on Polymerase Chain Reaction (PCR) and semi-selective agar such as CHROMagar™ STEC (CHROMagar). The implementation of gastrointestinal (GI) PCR assays in diagnostic laboratories began in December 2013, and by December 2019 around 40% of laboratories in England had adopted this approach. Consequently, there has been a substantial increase in the detection of non-O157 STEC cases. However, PCR is not universally used for detection of non-O157 STEC, and therefore the true incidence remains unknown.

Amongst STEC serogroups variation exists in their associations with severe disease. This is likely explained by differences in the virulence factors produced by different strains. STEC can produce 2 Shiga toxins (stx), stx1 (subtypes 1a, 1c and 1d) or stx2 (of which there are 7 subtypes stx2a–2g). Strains of STEC producing stx2, specifically subtypes stx2a and stx2d, are more likely to be associated with progression to HUS (1, 7). Intimin, encoded by the eae gene, is an adherence pathogenicity factor present in strains of STEC O157, and a proportion of non-O157 STEC.

The increasing notifications of non-O157 STEC has led to the need to prioritise the public health actions due to insufficient resources to follow up all cases. Risk assessment, based on clinical symptoms, risk group of the patient and potential pathogenicity of the strain of STEC infecting the patient, is challenging. In response, the Public Health Operational Guidance for Shiga toxin producing Escherichia coli (STEC) for the public health management of O157 and non-O157 STEC cases (including an algorithm to assist in follow up decision making) were updated and published in January 2023.

National enhanced surveillance of STEC in England has been ongoing since 2009. This report summarises the epidemiological data on confirmed cases of STEC O157 and non-O157 STEC cases in England in 2023 and compares this data to previous years.

Methods

The National Enhanced Surveillance System for STEC (NESSS) infection in England began in January 2009 to provide a rapid review of common exposures, record clinical outcomes and to supplement our understanding of the epidemiology of STEC infection. The system collects a standard dataset of clinical, epidemiological and microbiological data for all STEC cases, to improve outbreak recognition and facilitate and prioritise public health investigations. The data is collected from enhanced surveillance questionnaires (ESQ) and reconciled with laboratory reports associated with cases.

STEC is notifiable under the Health Protection (Notification) Regulations 2010. In England, local diagnostic laboratories report presumptive cases of STEC to UKHSA Health Protection Teams (HPTs) and then refer samples to the Gastrointestinal Bacteria Reference Unit (GBRU) for confirmation and further testing. GBRU reports the microbiological profile, including serogroup, virulence profile and single nucleotide polymorphism (SNP) type of the samples, which is derived through Whole Genome Sequencing (WGS). Depending on the virulence profile of the STEC strain and the outlined healthcare management process under the Operational Guidance algorithm, each HPT arranges for ESQ to be completed to obtain a detailed history of exposures 7 days prior to onset of illness. The ESQ collects: demographic details; risk status; clinical conditions, exposures including travel, food and water consumption, environmental exposures and outbreak status. Completed ESQs are submitted to the National Gastrointestinal Infections team at UKHSA to be included in NESSS.

For cases resident in England data included in this report were validated and extracted from NESSS and cases meeting the case definitions (see Table 1) were included in analyses.

Data from the 2023 Office for National Statistics (ONS) mid-year population estimates were used to provide denominators for the calculation of incidence rates. All dates for the figures are based on the receipt date of a sample specimen at the GBRU.

In March 2020 the serological testing method for diagnostic detection of STEC at GBRU was discontinued, and so there were no probable cases with serological evidence of infection identified after this date. With this, since 2021, there is only one microbiological case definition: a confirmed case is positive STEC culture confirmed by GBRU. Epidemiological case definitions are described in Table 1 below.

Table 1: Epidemiological case definitions

Classification	Definition
Primary	A symptomatic case with no history of close contact with a confirmed case in the 7 days prior to onset of illness
Co-primary	A symptomatic case with a date of onset within 3 days of another case where the exposure is believed to be through exposure to the same vehicle and not through social contact
Secondary	Case with a date of onset more than 4 days after the primary case or where transmission is believed to be through exposure to a primary case
Unsure	It is not possible to determine whether the case is primary or secondary with the information available. This may be because the patient was lost to follow-up, is asymptomatic or in an outbreak where it is not possible to identify the primary cases
Travel-associated	Case who has reported any travel outside of the UK in the 7 days prior to their date of onset of illness
Asymptomatic	A person from whom STEC was identified through contact screening procedures but who is asymptomatic

Data

Cases of STEC in England in 2023

In 2023, 2,018 culture-confirmed cases of STEC were reported in England, a decrease of 2% compared to 2022; these comprised 533 culture-confirmed cases of STEC serogroup O157 and 1,485 cases where a serogroup other than O157 was isolated (non-O157). For a further 775 cases, faecal specimens were confirmed as STEC by testing positive by PCR for stx genes, but STEC could not be detected on culture.

Twenty-five confirmed cases were infected with multiple serotypes of STEC. The most commonly reported serotypes in a co-infection were O157:H7 (n=7), O146:H21 (n=5) and O26:H11 (n=3) (Appendix 1).

STEC O157 cases in England

The crude incidence rate of confirmed STEC O157 in England had decreased from 2014 to 2021 but increased in again 2022. The rate for 2023 was lower than 2022 (Figure 1), the higher rate in 2022 likely explained by an STEC O157 outbreak in 2022 which was the largest detected since the start of routine WGS (8). In 2023, the crude incidence rate was 0.92 per 100,000 population (95% CI 0.85 to 1.01), which was comparable to pre-pandemic rates in 2019.

The highest incidence of STEC O157 was in the East of England (1.14 cases per 100,000 population, 95% CI 0.90 to 1.44) and the lowest was in the West Midlands (0.54 cases per 100,000 population, 95% CI 0.37 to 0.76) (Figure 2).

Figure 1: Incidence of Shiga toxin-producing Escherichia coli (STEC) O157 culture-confirmed cases by year, England, 2014 to 2023

Figure 2: Incidence of STEC O157 in England by region, 2023

Age, gender and seasonality of STEC O157 cases

Of 533 confirmed STEC O157 cases in England, 275 (51.5%) were female. In 2023, children aged 1 to 4 years had the highest incidence of infection (4.01 per 100,000 population, CI 3.27 to 4.88) (Figure 3).

Figure 3: Age-sex specific incidence rate of STEC O157 cases in England, 2023

STEC O157 infections in England display a distinct seasonality with an increase in infections in the summer months (from May to August) and a decline from September onwards (Figure 4). The 2023 trend data did not exceed the 5-year maximum, that was set by high rates in 2022. In 2023, the number of reported STEC O157 infections did follow similar trends to the 5-year median and was higher than the COVID-19 years (2020 to 2021).

Figure 4: Seasonal trend of laboratory confirmed cases of STEC O157 in England, 2016 to 2023

Clinical presentation and severity of illness

While the number of STEC O157 cases has fluctuated since 2015, the proportion of cases completing an ESQ has remained above 90% (Figure 5). Of the 533 confirmed STEC O157 cases in England in 2023, ESQs were received for 494 (92.7%), which was the lowest completion rate outside of the COVID-19 years 2020 and 2021.

Symptoms were reported for 483 out of 494 cases with an ESQ (97.8%), and 11 cases were asymptomatic; the majority of which reported diarrhoea (92.9%, n=459), abdominal pain (75.9%, n=375), and bloody stools (54.5%, n=269) (Table 2).

Hospitalisation was reported by 28.3% (n=140) of cases; duration of hospitalisation ranged from 0 to 13 days with median stay of 3 days. There was 1 death reported among STEC O157 cases (adult female).

During 2023, HUS occurred in 11 confirmed cases (2.1%), nearly two-thirds of which were under 5 years of age (n=7, 63.6%), with a median age of 3 years (range 1 to 57 years old). The incidence of STEC O157 HUS in children under 5 years in 2023 was 0.23 per 100,000 cases per population (CI 0.09 to 0.47).

Figure 5: The number of confirmed STEC O157 cases and percentage of enhanced surveillance questionnaires received in England, 2023

Table 2: Symptoms most frequently reported by STEC O157 cases, 2023

Symptom	Number and percentage of STEC O157 cases
Diarrhoea	459, 92.9%
Bloody stools	269, 54.5%
Abdominal pain	375, 75.9%
Nausea	220, 44.5%
Vomiting	145, 29.4%
Fever	158, 3.9%

Transmission routes

The natural reservoir of STEC is the gastrointestinal tract of ruminant animals, predominantly cattle and sheep. Human infections occur through direct contact with infected animals or their environment, consumption of contaminated food or water, or through contact with an infected individual (9). Previous case and outbreak investigations have attributed STEC infections to: farm visits; walks in the countryside, floodwater; raw milk and raw milk products like cheese and ice cream; salad leaves; and beef.

In England, of the 494 confirmed cases for whom ESQs were received during 2023, there were 472 (95.5%) primary or co-primary cases, 11 secondary cases (2.2%), and 11 unsure (2.2%).

An increase in travel-related cases was observed with 114 cases (23.1%) reporting travel abroad during their incubation period (7 days prior to onset), compared to 17.6% in 2022, but remaining lower that 2018 and 2019 (28% and 31% respectively). Of those 114 cases, only 31 spent their entire incubation period abroad.

Frequently reported subtypes of STEC O157

Among 533 isolates from confirmed STEC O157 cases in England in 2023, most had stx2 only (58.9%, n=314), followed by stx1+ stx2 (40.7%, n=217), and stx1 only (0.4%, n=2). stx2a, the subtype most likely to cause severe clinical presentation and HUS, was present in 42.0% of cases (n=224). The presence of stx2 only in 2023 has increased compared to 2022 (58.9% in 2023 compared to 46.9% in 2022).

Non-O157 STEC cases in England

Historically, cases of non-O157 STEC have been under ascertained, with 89 cases of STEC non-O157 reported over the 5-year period 2009 to 2013, prior to enteric PCR implementation.

Following the increase in recent years in diagnostic laboratories using PCR, there has been a significant increase in the detection of non-O157 STEC in England. Due to limited information on testing coverage at the diagnostic laboratories, it is not possible to calculate the true denominator, therefore an estimated incidence for non-O157 STEC is presented in this report.

In 2023, there were 1,485 culture-confirmed STEC non-O157 cases, and a further 775 were PCR positive but STEC could not be cultured. It is estimated that most stx PCR-positive, culture-negative specimens correspond to STEC non-O157, leading to an estimated total of 2,260 STEC non-O157 cases in England in 2023, an increase of 13.7% compared to 2022 (n=1,988). This number was above pre-pandemic levels, with an increase of 125.6% compared to 2019. Of 1,485 culture-positive STEC non-O157 cases, 87 different serogroups were confirmed by WGS. For 46 isolates, a serotype could not be identified as the genes encoding the somatic O antigen did not match any known sequence in the database.

In England, the 5 most common STEC non-O157 serogroups isolated from the 1,485 culture-confirmed cases in 2023 were O26 (n=256, 17.2%) followed by O146 (n=211, 14.2%), O91 (n=152, 10.2%), O145 (n=120, 8.1%), O128 (n=89, 6.0%) (Appendix 2).

In 2023, ESQ’s were received for 33.4% (n=755 of 2,260) of non-O157 STEC cases (Figure 6). Of these, 42.9% (n=638 of 1,485) were for culture positive non-O157 STEC cases, and 15.5% (n=117 of 755) of STEC cases confirmed only by PCR.

Between 2016 and 2019, there was a decline of 24% in the number of ESQs received for STEC non-O157 cases. This was thought to likely be associated with increasing numbers necessitating prioritisation and the implementation of algorithms in the 2018 guidance. Since a low of 26.6% in 2019, the percentage of non-O157 cases for which an ESQ was received has increased to 33.4% in 2023. The prioritisation algorithm for non-O157 follow up varies, dependent on serotype and stx subtype. Therefore, with more testing and diagnostic measures implemented, there are increases in cases and consequently a higher burden on case follow up.  

Of 2,260 STEC non-O157 cases in England, 1,230 (54.4%) were female. In 2023, children aged under 1 year had the highest incidence of infection (12.74 per 100,000 population, CI 9.98 to 16.01) (Figure 7).

Figure 6: The number of STEC non-O157 cases and percentage of enhanced surveillance questionnaires received in England, 2023

Figure 7: Age-sex specific incidence rate of STEC non-O157 cases in England, 2023

STEC non-O157 infections in England in 2023 displayed a distinct seasonality compared to STEC O157, with the peak of infection in September (Figure 8). This is later than the typically observed O157 seasonal trend which usually peaks during the summer months. The 2023 data exceeded the previous years median and maximum case rate.

Figure 8: Seasonal trend of laboratory confirmed cases of non-O157 STEC in England, 2016 to 2023

Clinical presentation and severity of illness

Of the 755 cases with clinical information, n=726 (96.2%) were symptomatic. Among the symptomatic cases, 88.3% reported diarrhoea (n=641), 71.3% abdominal pain (n=518) and 47.7% bloody stools (n=346) (Table 3). In total, 233 cases (32.1%) were hospitalised.

HUS occurred in 1.7% (39 of 2,260) of STEC non-O157 cases. From these 39 cases, the most frequently isolated serogroups were O26 (66.7%, n=26) and O145 (n=3, 7.7%). The remaining serogroups had 1 count each: O117, O146, O183, O45, O71. Serogroup was unavailable for 5 cases (12.8%), all (100%) were culture negative. STEC non-O157 HUS case age ranged from 0 to 72 years of age and 48.7% (n=19) were between 1 and 4 years of age. There were 2 deaths reported among cases of non-O157 STEC (both adults).

Table 3: Symptoms most frequently reported by STEC non-O157 cases in 2023

Symptom	Number and percentage of STEC non-O157 cases
Diarrhoea	641, 88.3%
Bloody stools	346, 47.7%
Abdominal pain	518, 71.3%
Nausea	307, 42.3%
Vomiting	233, 32.1%
Fever	227, 31.3%

Among all 2,260 non-O157 STEC cases in England in 2023, 41.2% (n=930) possessed the stx1 toxin alone, 30.2% (n=682) possessed stx2 alone and 28.7% (n=648) possessed both stx1 and stx2. Of these 2,260 cases, 848 (37.5%) had the eae gene.

Among the 1,485 culture-confirmed STEC non-O157 cases, stx1a only was detected in 22.9% (n=341) of cases, stx1c only in 17.7% (n=263) of cases, stx2a only in 16.8% (n=249) of cases, stx2b only in 9.8% (n=145) of cases (Figure 9, Appendix 2).

Figure 9: Prevalence of stx subtype combinations reported amongst the top 10 non-O157 STEC serogroups in England, 2023

Increase of non-O157 STEC

In England, a shift in the burden of disease from notifications of STEC O157 cases to non-O157 STECs has been observed in recent years, with the trend continuing in 2023 (Figure 10). While the notifications of STEC O157 have declined, notifications of STEC non-O157 have increased twofold (139%) since 2018, resulting in an overall increase in STEC notifications and the burden placed on public health and clinical services. Serogroups O26 and O145 are drivers of the increase in STEC non-O157 cases (10).

Figure 10: Percentage of laboratory confirmed STEC cases in England by serogroup, 2015 to 2023

STEC O26 cases in England

Questionnaires were received for 91.8% (n=235) of all 256 confirmed STEC O26 cases. Of the 235, there were 91.2% (n=214) cases that were symptomatic. Of those symptomatic, diarrhoea was reported in 92.1% (n=197), 62.6% (n=134) reported abdominal pain, and 46.7% (n=100) reported bloody stools (Table 4).

Overall, in 2023 a slightly higher proportion of STEC O26 cases (32.2%, n=69) were hospitalised compared to STEC O157 cases 28.3% (n=140).

Ten percent (n=26) of confirmed STEC O26 cases developed HUS as compared to 2.1% of confirmed STEC O157 cases (n=11).

Table 4: Symptoms most frequently reported by STEC O26 cases in 2023

Symptom	Number and percentage of STEC O26 cases
Diarrhoea	197, 92.1%
Bloody stools	100, 46.7%
Abdominal pain	134, 62.6%
Nausea	69, 32.2%
Vomiting	100, 46.7%
Fever	63, 29.4%

Of the 256 STEC O26 cases in England, 136 (53.1%) were female. Children aged 1 to 4 years of age comprised 39.1% (n=100) of cases (Figure 11).

Figure 11: Age-sex specific incidence rate of STEC O26 cases in England, 2023

STEC O145 cases in England

Questionnaires were received for 91.7% (n=110) of all 120 confirmed STEC O145 cases. Of the 109 (99.1%) cases that were symptomatic, 90.8% (n=99) cases had diarrhoea, 89.9% (n=98) reported abdominal pain, 67.9% (n=74) bloody stools and 56.9% (n=62) nausea. Overall, in 2023 a higher proportion of STEC O145 cases (44.0%, n=48) were hospitalised compared to STEC O157 cases 28.3% (n=140), and a similar proportion of HUS was reported in O145 cases with 2.5% (n=3) compared to 2.1% in O157 cases (n=11).

Of 120 STEC O145 cases in England, 59% (n=71) were female. The 20 to 29 age group comprised of 21% (n=25) of cases (Figure 12).

Figure 12: Age-sex specific incidence rate of STEC O145 cases in England, 2023

Outbreaks

STEC outbreaks investigated in England during 2023

Typically, an exceedance is investigated when 10 or more cases fall within the same 5 SNP single linkage cluster for clinically severe serotypes, or an outbreak may be declared if cases are linked to common exposure, such as visiting the same petting farm, attending the same nursery or reporting consumption of the same food item. However, an investigation may be undertaken after considering a number of factors, including the number of persons affected, temporal and geographic distribution, clinical severity, and the microbiological characteristics of the STEC strain.

Seven STEC outbreaks affecting 228 people, 145 of whom were resident in England, were investigated in 2023. One outbreak was caused by O157; the other 6 outbreaks were caused by STEC O26, O145, and O183 (Table 5). There was 1 death and 21 HUS cases reported to be associated with STEC outbreaks in 2023. A suspected or confirmed vehicles was identified for all seven outbreaks. Five were identified through analytical studies or pathogen detection in a food isolate, while 2 had a lower level of certainty, as it was suspected based solely on questionnaire data (Table 5).

Table 5: STEC O157 and non-O157 foodborne outbreaks in England, 2023

Agent	Total laboratory confirmed cases (n)	Source
STEC O157 t5.7510 stx1a stx2a eae positive	5 (4 of which in England)	Confirmed beef product (Note 1)
STEC O26 t5.2283 stx2a eae positive	37 (18 of which in England)	Confirmed dried fruit product (Note 1)
STEC O26 t5.2224 stx1a eae positive	33 (17 of which in England)	Suspected salad leaves (Note 1)
STEC O145 t5.206 stx2a eae positive	44 (26 of which in England)	Suspected fresh produce (Note 2)
STEC O145 t5.456 stx2a eae positive	47 (31 of which in England)	Suspected salad leaves (Note 2)
STEC O145 t5.405 stx2a eae positive	36 (28 of which in England)	Confirmed unpasteurised cheese (Note 1)
STEC O183 t5.5 stx2a eae negative	26 (21 of which in England)	Suspected beef product (Note 1)

Note 1: Identified through analytical studies, food isolates testing or food chain investigations. Note 2: Identified though food exposure data only.

STEC O157 outbreak

UKHSA and public health agencies in devolved administrations (DAs) investigated an outbreak of STEC O157 stx1a stx2a eae positive. There were 5 confirmed cases of which 4 cases resided in England, all completed an ESQ; 80% of cases reported bloody stools (n=4), 40% were admitted to hospital (n=2). The median age was 20 years. None of the cases reported to have developed HUS and no cases associated with this cluster died. Food chain investigations and descriptive epidemiological investigations identified a beef product as confirmed vehicle for this outbreak. A beef food isolate also fell within the same 5-SNP cluster as the cases.

STEC O26 outbreaks

Two STEC O26 outbreaks were investigated in 2023.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O26 stx2a eae positive. There were 37 confirmed cases, of which 18 were resident in England. The median age was 3 years. ESQs containing clinical and exposure information were available for all cases (n=37). Overall, 59.5% of cases reported blood in stools (n=22), 18 were hospitalised (48.7%), 46.0% developed HUS (n=17). No deaths were reported. Epidemiological and food chain investigations identified a dried food product as confirmed vehicle of infection.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O26 stx1a eae positive. There were 33 confirmed cases of which 17 cases resided in England. Questionnaires were received for 30 (91.0%) of cases. The median age was 47 years. Twenty-four cases reported bloody diarrhoea (80.0%) and 8 cases reported hospitalisation for their symptoms (26.7%); there were no reports of HUS or deaths. Epidemiological and food chain investigations identified salad leaves as the likely vehicle of infection.

STEC O145 outbreaks

Three STEC O145 outbreaks were investigated in 2023.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O145 stx2a eae positive. There were 44 cases associated with the outbreak (26 cases resided in England), all of which were laboratory confirmed at the 5-SNP level. The median age was 35 years. ESQs were completed for 42 of the 44 confirmed cases (95.5%). Overall, 78.6% of cases reported blood in stools (n=33) and 21 were hospitalised (50.0%). There were 2 reports of HUS but no deaths in association with this outbreak. Epidemiological investigations (descriptive data of food exposures) were undertaken, and a fresh produce was identified as suspected vehicle of infection though food chain investigations were inconclusive.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O145 stx2a eae positive. There were 47 confirmed cases, of which 31 were resident in England. The median age was 30 years. ESQs containing clinical and exposure information were available for 40 cases. Overall, 75.0% of cases reported blood in stools (n=30), 18 were hospitalised (45.0%), but none developed HUS. No deaths were reported. Epidemiological investigations (descriptive data of food exposures) were undertaken and salad leaves were identified as suspected vehicle of infection though food chain investigations and analytical studies were inconclusive.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O145 stx2a eae positive (11). There were 36 confirmed cases, of which 28 were resident in England. The median age was 36 years. ESQs containing clinical and exposure information were available for 31 cases. Overall, 64.5% of cases reported blood in stools (n=20), 15 were hospitalised (48.4%). One case developed HUS and died. Epidemiological, food chain and microbiological investigations identified an unpasteurised cheese as confirmed vehicle of infection.

Other outbreaks

UKHSA and public health agencies in DAs investigated an outbreak of STEC O183 stx2a eae negative (12). There were 26 confirmed cases, of which 21 were resident in England. The median age was 17 years. ESQs containing clinical and exposure information were available for 24 cases. Overall, 70.8% of cases reported blood in stools (n=17), 6 were hospitalised (25.0%), and 1 developed HUS. One death was reported to be associated with this outbreak. Epidemiological and food chain investigations identified a beef product as the likely vehicle of infection.

Conclusions

The number of STEC case notifications to national surveillance continued to increase into 2023, driven by non-O157 STEC. In recent years the number of O157 confirmed cases has been on a downward trajectory; with the number of 2023 cases similar to pre-COVID-19  rates in 2019. The 2023 O157 rates are lower than in 2022, likely due to the large STEC O157 outbreak in 2022.

The STEC O157 in 2023 seasonality displays a rounded pattern, with a steady increase in the early summer and decline into winter. The non-O157 STEC seasonality in 2023 increased earlier in the year than STEC O157 and appears to remain at high rates in the winter months, unlike O157.

The age-sex distribution of O157 infections was similar to 2022, where the highest incidence was in the 1 to 4 years. While the percentage of STEC O157 cases who developed HUS remained similar at 2.1%, the percentage of cases hospitalised for their illness decreased slightly in 2023 compared to 2022 (28.3% and 30.9% respectively) returning to similar levels from pre-pandemic years.

The detection of non-O157 STEC infections has continued to increase since 2021, continuing the trend observed in pre-COVID-19 years. Similar to 2022, the most common non-O157 serogroup detected in 2023 was STEC O26 and cases infected with this serogroup had a higher proportion (10.2%) of HUS than O157 cases (2.1%).

The trends in the 2023 report continue to demonstrate the increase of non-O157 STEC. While trends are impacted by 7 outbreaks, increases in testing methods in the regions will increase STEC detection and therefore rates. Salad leaves and fresh produce continue to be an important source of STEC outbreaks and specific interventions targeting this food product are important to prevent further outbreaks. It is likely that the interventions during the COVID-19 pandemic are having less of an impact on the incidence of STEC cases, and the true trends and STEC epidemiology changes are restoring back to pre-pandemic rates.

Appendix 1

Confirmed cases with co-infections

Serotype 1	Serotype 2	Stx profiles | eae | CC	Cases (n)
O157:H7	O38:H26	stx2a | stx1c eae+ | eae- CC11 | CC10	1
O157:H7	O100:H20	stx1a,stx2c | stx2e eae+ | eae- CC11 | CC2514	1
O157:H7	O145:H28	stx2a | stx2a eae+ | eae+ CC11 | CC29	1
O157:H7	O157:H11	stx2a | stx2a eae+ | eae+ CC11 | CC11	1
O157:H7	O26:H11	stx2c | stx2a + stx1a,stx2a eae+ | eae+ CC11 | CC29	2
O157:H7	O153-O178:H7	stx1a,stx2a | stx1c eae+ | eae- CC11 | CC278	1
O146:H21	O145:H28	stx1c | stx2a eae- | eae+ CC442 | CC32	1
O146:H21	O38:H26	stx1c | stx1c,stx2b eae- | eae- CC442 | CC10	1
O146:H21	O113:H4	stx1c | stx1c,stx2b eae- | eae- CC442 | CC10	1
O146:H21	O149:H2	stx1c | stx2b eae- | eae-	1
O146:H21	O91:H14	stx1c | stx1a,stx2b eae- | eae- CC442 | CC33	1
O26:H11	O63:H6	stx2a | stx2f eae+ | eae+	1
O26:H11	O91:H14	stx1a | stx1a,stx2b eae+ | eae- CC21 | CC33	1
O146:H28	O156:H25	stx2b | stx1a eae- | eae+	1
O181:H16	O103:H2	stx1c,stx2b | stx1a eae- | eae+	1
O181:H16	O71:H2	stx1c,stx2b | stx1a eae- | eae+	1
O123:H2	O177:H11	stx1a | stx1c eae+ | eae+	1
O136:H20	O166:H28	stx1c | stx2b eae- | eae-	1
O100:H30	O104:H7	stx2g | stx1c eae- | eae-	1
O181:H16	O71:H2	stx1c,stx2b | stx1a eae- | eae+	1
O123:H10	O22:H14	stx1c,stx2b | stx2b eae- | eae-	1
O8:H19	O93:H19	stx2a | stx2a,stx2e eae- | eae-	1
O91:H14	O149:H2	stx1a,stx2b | stx2b eae- | eae-	1
O103:H8	O76:H7	stx2a | stx2a eae+ | eae+ CC29 | CC278	1

Appendix 2

Prevalence of stx subtype combination reported amongst the top 10 non-O157 STEC serogroups in England, 2023

Serogroup	Stx Subtype	n	Percentage
O103 (n=42)	stx1a	34	81
	stx1a;stx2a	3	7
	stx2a	5	12
O111 (n=25)	stx1a	22	88
	stx1a;stx2a	2	8
	stx2a	1	4
O113 (n=27)	stx1c	1	4
	stx1c;stx2b	22	81
	stx1c;stx2d;stx2b	1	4
	stx2a;stx2c	1	4
	stx2b	1	4
	stx2d	1	4
O117 (n=59)	stx1a	57	97
	stx1c	1	2
	stx2b	1	2
O128 (n=89)	stx1a	2	2
	stx1c	3	3
	stx1c;stx2b	56	63
	stx1c;stx2d;stx2b	1	1
	stx2b	25	28
	stx2f	2	2
O145 (n=120)	stx2a	118	98
	stx2f	2	2
O146 (n=211)	stx1a	1	0
	stx1a;stx1c	1	0
	stx1a;stx1c;stx2b	1	0
	stx1c	103	49
	stx1c;stx2b	60	28
	stx1c;stx2d;stx2b	1	0
	stx2a;stx1c;stx2b	1	0
	stx2b	41	19
	stx2c	1	0
	stx2d	1	0
O26 (n=254)	stx1a	128	50
	stx1a;stx2a	35	14
	stx2a	91	36
O76 (n=39)	stx1c	29	74
	stx1c;stx2b	10	26
O91 (n=152)	stx1a	7	5
	stx1a;stx2b	121	80
	stx1a;stx2b;stx2d	1	1
	stx1c;stx2b	1	1
	stx2b	22	14

UKHSA STEC publications in 2023

1. Den Ouden A, Greig DR, Rodwell EV, Tripodo F, Olonade I, Swift C, Jenkins C. ‘Escherichia coli encoding Shiga toxin subtype Stx2f causing human infections in England, 2015-2022’ Journal of Medical Microbiology 2023: volume 72, issue 6
2. Byrne L, Douglas A, Launders N, Godbole G, Lynn R, Inward C, Jenkins C. ‘Haemolytic uraemic syndrome in children England, Wales, Northern Ireland, and Ireland: A prospective cohort study’ Epidemiology and Infection 2023: volume 151, e160
3. Greig DR, Do Nascimento V, Olonade I, Swift C, Nair S, Jenkins C. ‘Surveillance of antimicrobial resistant Shiga toxin-producing E. coli O157:H7 in England, 2016-2020’ Journal of Antimicrobial Chemotherapy 2023: volume 78, issue 9, 2263-2273
4. Rodwell EV, Simpson A, Chan YW, Godbole G, McCarthy ND, Jenkins C. ‘The epidemiology of Shiga toxin-producing Escherichia coli O26:H11 (clonal complex 29) in England, 2014-2021’ Journal of Infection 2023: volume 86, issue 6, 552-562

Data caveats

This report was produced using laboratory data for England only. Therefore, the number of Shiga toxin-producing Escherichia coli laboratory reports published in previous reports which include data from other UK countries will be higher than those included in this report.

Acknowledgements

We are grateful to:

• the NHS and independent sector microbiology teams, local authorities and local health protection and environmental health specialists who contribute data and reports to the national enhanced surveillance system for STEC (NESSS)

• the epidemiologists and information officers who have worked on NESSS

• staff in the Gastrointestinal Bacterial Reference Unit (GBRU) for providing the Reference Laboratory Services and laboratory surveillance functions and expertise

• UKHSA Regional and Collaborating Public Health Laboratories and Food Water and Environmental Microbiology Services for providing a surveillance function for GI pathogens and testing of food and environmental samples during outbreak investigations

Prepared by: Gastrointestinal Infections, Food Safety and One Health  Division, UKHSA

For queries relating to this document, please contact: VTEC@ukhsa.gov.uk

References

1. Launders N, Byrne L, Jenkins C, Harker K, Charlett A, Adak GK. ‘Disease severity of Shiga toxin-producing E. coli O157 and factors influencing the development of typical haemolytic uraemic syndrome: a retrospective cohort study, 2009-2012’ BMJ Open 2016: volume 6, issue 1, e009933
2. Dodd CC, Cooper MJ. ‘Multidisciplinary response to the Escherichia coli 0104 outbreak in Europe’ Military Medicine 2012: volume 177, issue 11, 1406-10
3. Launders N, Byrne L, Adams N, Glen K, Jenkins C, Tubin-Delic D, Locking M, Williams C, Morgan D; Outbreak Control Team. ‘Outbreak of Shiga toxin-producing E. coli O157 associated with consumption of watercress, United Kingdom, August to September 2013’ Eurosurveillance 2013: volume 18, issue 44, 20624
4. Gobin M, Hawker J, Cleary P, Inns T, Gardiner D, Mikhail A, McCormick J, Elson R, Ready D, Dallman T, Roddick I, Hall I, Willis C, Crook P, Godbole G, Tubin-Delic D, Oliver I. ‘National outbreak of Shiga toxin-producing Escherichia coli O157:H7 linked to mixed salad leaves, United Kingdom, 2016’ Eurosurveillance 2018: volume 23, issue 18, 17-00197
5. Byrne L, Adams N, Jenkins C. ‘Association between Shiga Toxin-Producing Escherichia coli O157:H7 stx Gene Subtype and Disease Severity, England, 2009-2019’ Emerging Infectious Diseases 2020: volume 26, issue 10, 2394-2400
6. Vishram B, Jenkins C, Greig DR, Godbole G, Carroll K, Balasegaram S, Byrne L. ‘The emerging importance of Shiga toxin-producing Escherichia coli other than serogroup O157 in England’ Journal of Medical Microbiology 2021: volume 70, issue 7, 001375
7. Brandal LT, Wester AL, Lange H, Løbersli I, Lindstedt BA, Vold L, Kapperud G. ‘Shiga toxin-producing escherichia coli infections in Norway, 1992-2012: characterization of isolates and identification of risk factors for haemolytic uremic syndrome’ BMC Infectious Diseases 2015: volume 15, 324
8. Cunningham N, Jenkins C, Williams S, Garner J, Eggen B, Douglas A, Potter T, Wilson A, Leonardi G, Larkin L, Hopkins S. ‘An outbreak of Shiga toxin-producing Escherichia coli (STEC) O157:H7 associated with contaminated lettuce and the cascading risks from climate change, the United Kingdom, August to September 2022’. Eurosurveillance 2024: volume 29, issue 36, 2400161
9. Butt S, Jenkins C, Godbole G, Byrne L. ‘The epidemiology of Shiga toxin-producing Escherichia coli serogroup O157 in England, 2009-2019’ Epidemiology and Infection 2022: volume150, e52
10. Rodwell EV, Chan YW, Sawyer C, Carroll A, McNamara E, Allison L, Browning L, Holmes A, Godbole G, McCarthy N, Jenkins C. ‘Shiga toxin-producing Escherichia coli clonal complex 32, including serotype O145:H28, in the UK and Ireland’ Journal of Medical Microbiology 2022: volume 71, issue 8
11. Quinn OI, Jenkins C, Greig DR, Neale S, Jorgensen F, Yanshi, Inns T, Allison L, Browning L, Douglas A, Balasegram S. ‘An outbreak of Shiga Toxin-producing Escherichia coli Serotype O145:H28 Associated with Domestic Travel and Consumption of Unpasteurized Cheese, UK, 2023’ Journal of Food Protection 2025: volume 88, issue 4, 100470
12. Greig DR, Quinn OI, Rodwell EV, Olonade I, Swift C, Douglas A, Balasegram S, Jenkins C. ‘Genomic analysis of an outbreak of Shiga toxin-producing Escherichia coli O183:H18 in the United Kingdom, 2023’ Microbial Genomics 2024: volume 10, issue 5, 001243