Research and analysis

Shiga toxin-producing Escherichia coli (STEC) data: 2024

Updated 30 July 2025

Main points for 2024

The main points of the 2024 annual report are:

1. Overall, 2,544 cultured-confirmed cases of Shiga toxin-producing Escherichia coli (STEC) were reported in England during 2024, 564 were STEC O157 and 1,980 were STEC non-O157. This is an increase of 26.1% compared to 2023. This increase was partly due to an outbreak of STEC O145 with 196 confirmed cases in England in 2024.

2. A total of 564 culture-confirmed cases of STEC O157 were reported in England in 2024 compared to 533 in 2023, an increase of 5.8%. A total of 2,762 cases of STEC non-O157 were reported in England in 2024 (including 1,980 culture-confirmed cases and 782 faecal specimens positive for stx genes on polymerase chain reaction (PCR) but culture-negative), an increase of 22.2% compared to 2023. Among culture-confirmed non-O157 cases, the most commonly isolated serogroup was STEC O26 (356 of 1,980, or 18.0%).

3. As in 2023, children aged 1 to 4 years had the highest annual incidence of infection for STEC O157 (84 cases in 2024, 3.37 per 100,000 population, 95% confidence interval (CI) 2.69 to 4.17). Children aged 1 to 4 years also had the highest annual incidence of infection due to STEC non-O157 in 2024 (273 cases in 2024, 10.96 per 100,000 population, 95% CI 9.70 to 12.34), compared to children aged under 1 year having the highest incidence in 2023.

4. Where information was available, just under a third (140 of 509, or 27.5%) of confirmed STEC O157 cases and just over a third (364 of 1,060, or 34.3%) of STEC non-O157 cases in England were hospitalised. The proportions of hospitalisations for STEC O157 and STEC non-O157 were comparable to the previous year. Two deaths were reported among STEC O157 cases and 5 deaths among STEC non-O157 cases.

5. Where information was available, 2.1% of STEC O157 cases (12 of 564) and 1.7% (46 of 2,762) of STEC non-O157 reported developing haemolytic uraemic syndrome (HUS). As in 2023, approximately 10% (30) of confirmed STEC O26 cases developed HUS.

6. In 2024, the national team investigated 5 outbreaks of STEC. These involved 467 cases, 348 of whom were resident in England. All outbreaks were attributable to non-O157 STEC: 3 outbreaks involved STEC O26, 1 involved STEC O145 and 1 involved STEC O103. A suspected or confirmed vehicle was identified for 3 of the 5 outbreaks and included beef, fresh fruit and salad leaves.

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 faeces, consumption of contaminated food or water, and person-to-person spread (2). STEC infections can present as sporadic cases or as clusters and outbreaks. Large national and multinational outbreaks have been associated with foodborne transmission (3 to 5).

The most common serogroup of STEC notified to UKHSA in England is O157 (6), 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). Detection of non-O157 STEC requires a combination of molecular methods such as polymerase chain reaction (PCR) followed by culture on semi-selective chromogenic agar such as CHROMagar™ STEC (CHROMagar). Approximately 40% of laboratories in England have implemented the molecular methods, and therefore non-O157 STEC in England remains under-ascertained.

Among 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, 8) 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 was 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 2024 and compares this data to previous years.

Methods

The National Enhanced Surveillance System for STEC (NESSS) 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 data set 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 an 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
• 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 was used to provide denominators for the calculation of incidence rates as 2024 mid-year population estimates were not yet available at the time of publication of this report. All dates for the figures are based on the receipt date of a sample specimen at the 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 2024

In 2024, 2,544 cultured-confirmed cases of STEC were reported in England – an increase of 26.1% compared to 2023. These comprised 564 culture-confirmed cases of STEC serogroup O157 and 1,980 cases where a serogroup other than O157 was isolated (non-O157). For a further 782 cases, faecal specimens were confirmed as STEC by testing positive by PCR for stx genes, but STEC could not be cultured.

Thirty confirmed cases were infected with multiple serotypes of STEC. The most commonly reported co-infection serotypes were O157:H7 (13), O26:H11 (8) and O128:H2 (4) (Appendix 1).

STEC O157 cases in England

The crude incidence rate of confirmed STEC O157 in England had been following a decreasing trend between 2015 and 2021, but has increased in recent years (Figure 1). The rate for 2022 was inflated by an STEC O157 outbreak – the largest O157 outbreak detected since the start of routine WGS (9). In 2024, the crude incidence rate increased slightly compared to 2023, but remained comparable to pre-pandemic rates in 2019 (0.98 per 100,000 population in 2024, 95% CI 0.90 to 1.06).

The highest incidence of STEC O157 was in the North East (1.44 cases per 100,000 population, 95% CI 1.02 to 1.97) and the lowest was in the West Midlands (0.72 cases per 100,000 population, 95% CI 0.53 to 0.97) (Figure 2).

Figure 1. Incidence per 100,000 population of STEC O157 cases by year, England, 2015 to 2024

Figure 2. Incidence per 100,000 population of STEC O157 cases in England by region, 2024

In England, of the 519 confirmed cases for whom ESQs were received during 2024, there were 498 (96.0%) primary or co-primary cases, 11 secondary cases (2.1%) and 10 unsure (1.9%).

An increase in travel-related cases was observed, with 184 cases (35.5%) reporting travel abroad during their incubation period (7 days prior to onset), compared to 114 cases (23.1%) in 2023. Of those 184 cases, only 49 spent their entire incubation period abroad.

Age, gender and seasonality of STEC O157 cases

Overall, 327 (58.0%) of the 564 confirmed STEC O157 cases in England were female. In 2024, cases ranged in age from 0 to 93 years; children aged 1 to 4 years had the highest incidence of infection (84 cases in 2024, 3.37 per 100,000 population, CI 2.69 to 4.17) (Figure 3).

Figure 3. Age-sex specific incidence rate of STEC O157 cases in England, 2024

STEC O157 infections in England display a distinct seasonality with an increase in infections in the summer months (from May to September) and a decline from October onwards (Figure 4). The 2024 trend data did not exceed the 5-year maximum that was set by high rates in 2022. In 2024, the number of reported STEC O157 infections followed similar trends to the 5-year median and was higher than the SARS-CoV-2 years (2020 to 2021).

Figure 4. Seasonal trend of cases of STEC O157 in England, 2017 to 2024

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 564 confirmed STEC O157 cases in England in 2024, ESQs were received for 519 (92.0%), which was the lowest completion rate since 2015 outside of the SARS-CoV-2 years 2020.

Symptoms were reported for 509 out of 519 cases with an ESQ (98.1%). The remaining 10 cases were asymptomatic. The majority of symptomatic cases reported diarrhoea (471, or 92.5%), abdominal pain (405, or 79.6%) and bloody stools (273, or 53.6%) (Table 2).

Hospitalisation was reported by 27.5% (140) of symptomatic cases; duration of hospitalisation ranged from 0 to 9 days with a median stay of 2 days. There were 2 deaths reported among STEC O157 cases (both adults).

During 2024, HUS occurred in 12 confirmed cases (2.1%, 12 cases out of 564 cases with information available for HUS), 6 of which were under 5 years of age (50.0%), with a median age of 5.5 years (range: 1 to 74 years old). The incidence of STEC O157 HUS in children under 5 years in 2024 was 0.20 per 100,000 cases per population (CI: 0.07 to 0.43).

Figure 5. The number of STEC O157 cases and percentage of enhanced surveillance questionnaires received in England, 2024

Table 2. Symptoms most frequently reported by STEC O157 cases, 2024 (509)

Symptom	Number and percentage of STEC O157 cases
Diarrhoea	471, 92.5%
Abdominal pain	405, 79.6%
Bloody stools	273, 53.6%
Nausea	220, 43.2%
Fever	152, 29.9%
Vomiting	139, 27.3%

Frequently reported subtypes of STEC O157

Among 564 isolates from confirmed STEC O157 cases in England in 2024, most had stx2 only (294, or 52.1%), followed by stx1+ stx2 (264, or 46.8%) and stx1 only (6, or 1.1%). Stx2a, the subtype most likely to cause severe clinical presentation and HUS, was present in 31.9% of cases (180) – a slight decrease from 42.0% in 2023. The presence of stx2 only in 2024 has decreased compared to 2023 (52.1% in 2024 compared to 58.9% in 2023).

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 2024, there were 1,980 culture-confirmed STEC non-O157 cases and a further 782 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 2,762 STEC non-O157 cases in England in 2024, an increase of 22.2% compared to 2023 (which saw 2,260 cases). The number of cases in 2024 was above pre-pandemic levels, with an increase of 175.6% compared to 2019.

Of 1,980 culture-positive STEC non-O157 cases, 98 different serogroups were confirmed by WGS for 1,931 isolates. For 49 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 non-O157 STEC serogroups isolated from the 1,980 culture-confirmed cases in 2024 were O26 (356, or 18.0%), followed by O145 (247, or 12.5%), O146 (227, or 11.5%), O91 (159, or 8.0%) and O128 (115, or 5.8%) (Appendix 2). The increase in the number of STEC O145 cases in 2024 compared to 2023 was partially attributable to a large STEC O145 outbreak of over 200 cases.

In 2024, ESQs were received for 39.4% (1,088 of 2,762) of non-O157 STEC cases (Figure 6). Of the 1,980 cases of culture positive non-O157 STEC, 47.4% (939) had ESQs, compared to 19.1% (149) of the 782 STEC cases confirmed only by PCR.

Between 2016 and 2019, there was a decline of 29.1% in the percentage 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 39.4% in 2024.

Of 2,762 reported STEC non-O157 cases in England, 1,539 (55.7%) were female. In 2024, cases ranged in age from 0 to 98 years; children aged 1 to 4 years had the highest annual incidence of infection due to STEC non-O157 (273 cases in 2024, 10.96 per 100,000 population, 95% CI 9.70 to 12.34) (Figure 7), compared to children aged under 1 year in 2023.

Figure 6. The number of STEC non-O157 cases and percentage of enhanced surveillance questionnaires received in England, 2024

Figure 7. Age-sex specific incidence rate of STEC non-O157 cases in England, 2024

STEC non-O157 infections in England typically display a distinct seasonality, with the peak of infection in autumn, compared to the typically observed O157 seasonal trend which usually peaks during the summer months. However, in 2024, STEC non-O157 infections peaked in April and May, attributable to a large STEC O145 outbreak, and a second, smaller peak was observed in September as expected. Overall, the 2024 data exceeded the 5-year median and maximum case rate (with COVID-19 years, 2020 and 2021, excluded).

Figure 8. Seasonal trend of non-O157 STEC cases in England, 2017 to 2024

Clinical presentation and severity of illness

Of the 1,088 cases with clinical information, 97.4% (1,060) were symptomatic. Among the symptomatic cases, 89.3% reported diarrhoea (947), 73.6% abdominal pain (780) and 53.4% bloody stools (566) (Table 3). In total, 364 cases (34.3%) were hospitalised.

HUS occurred in 1.7% (46 of 2,762) of STEC non-O157 cases. From these 46 cases, the most frequently isolated serogroups were O26 (30, or 65.2%) and O145 (8, or 17.4%). The remaining serogroups had one case each: O103, O55 and O76. Serogroup was unavailable for 5 cases (10.9%), all of which (100.0%) were culture negative.

STEC non-O157 HUS cases ranged in age from 0 to 78 years; 39.1% (18) were aged between 1 and 4 years. There were 5 deaths reported among cases of non-O157 STEC (all adults).

Table 3. Symptoms most frequently reported by STEC non-O157 cases in 2024 (1,060)

Symptom	Number and percentage of STEC non-O157 cases
Diarrhoea	947, 89.3%
Abdominal pain	780, 73.6%
Bloody stools	566, 53.4%
Nausea	454, 42.8%
Vomiting	333, 31.4%
Fever	331, 31.2%

Among all 2,762 non-O157 STEC cases in England in 2024, 34.8% (962) possessed the stx1 toxin alone, 35.3% (976) possessed stx2 alone and 29.8% (824) possessed both stx1 and stx2. Of these 2,762 cases, 1,186 (42.9%) had the eae gene.

Among the 1,980 culture-confirmed STEC non-O157 cases, stx2a only was detected in 23.1% (457) of cases, stx1a only was detected in 20.0% (395) of cases, stx1c only in 13.9% (275) of cases and stx2b only in 9.4% (187) of cases (Figure 9, Appendix 2).

Figure 9. Prevalence of stx subtype combinations reported amongst the top 10 non-O157 STEC serogroups in England, 2024

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 2024 (Figure 10). While the notifications of STEC O157 have returned to pre-pandemic levels, notifications of STEC non-O157 have increased nearly 3-fold (175.6%) from 2019 to 2024, resulting in an overall increase in STEC notifications and the burden placed on public health and clinical services. Serogroups O26 and O145 have been driving the increase in STEC non-O157 cases [10].

Figure 10. Percentage of laboratory confirmed STEC cases in England by serogroup, 2015 to 2024

STEC O26 cases in England

Questionnaires were received for 89.6% (319) of all 356 confirmed STEC O26 cases. Of the 319, 94.7% (302) of cases were symptomatic. Of those symptomatic, diarrhoea was reported in 91.7% (277), 72.2% (218) reported abdominal pain and 49.7% (150) reported bloody stools (Table 4).

Overall, in 2024 a slightly higher proportion of STEC O26 cases (104, or 34.4%) were hospitalised compared to STEC O157 cases (140, or 27.5%).

Approximately one tenth (30 of 356, or 8.4%) of confirmed STEC O26 cases developed HUS, compared to 2.1% of confirmed STEC O157 cases (12 cases out of 564 cases with information available for HUS).

Table 4. Symptoms most frequently reported by STEC O26 cases in 2024 (302)

Symptom	Number and percentage of STEC O26 cases
Diarrhoea	277, 91.7%
Abdominal pain	218, 72.2%
Bloody stools	150, 49.7%
Nausea	140, 46.4%
Vomiting	113, 37.4%
Fever	105, 34.8%

Of the 356 STEC O26 cases in England in 2024, 59.0% (210) were female; children aged 1 to 4 years had the highest annual incidence of infection due to STEC O26 (4.78 per 100,000 population, 95% CI 3.96 to 5.72) (Figure 11), compared to children aged under one year having the highest incidence in 2023.

Figure 11. Age-sex specific incidence rate of STEC O26 cases in England, 2024

STEC O145 cases in England

Questionnaires were received for 90.7% (224) of all 247 confirmed STEC O145 cases. Of the 222 (89.9%) cases that were symptomatic, 96.0% (213) had diarrhoea, 86.5% (192) reported abdominal pain and 76.6% (170) reported bloody stools.

Overall, in 2024 a higher proportion of STEC O145 cases (105 of 222, or 47.3%) were hospitalised compared to STEC O157 cases (140 of 509, or 27.5%). Similarly, a slightly higher proportion of HUS was reported in O145 cases in 2024, with 3.2% (8 cases out of 224 cases with information for HUS) of O145 cases developing HUS compared to 2.1% of confirmed STEC O157 cases (12). Furthermore, the proportion of HUS among O145 cases in 2024 was slightly higher than in 2023 (3, or 2.5%).

Of 247 STEC O145 cases in England in 2024, 53.9% (133) were female; the 20 to 29 age group had the highest annual incidence of infection due to STEC O145 (0.95 per 100,000 population, 95% CI 0.74 to 1.21) (Figure 12), compared to children aged under 1 year having the highest incidence in 2023. The change in age distribution between 2023 and 2024 may be driven by the large STEC O145 outbreak in 2024.

Figure 12. Age-sex specific incidence rate of STEC O145 cases in England, 2024

Outbreaks

National STEC outbreaks investigated in England during 2024

Typically, an exceedance is investigated by the national team 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 a 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 for clusters of concern that are between 5 and 9 cases in size 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.

In 2024, the national team investigated 5 STEC outbreaks affecting 467 people, 348 of whom were resident in England. All outbreaks were attributable to non-O157 STEC: 3 outbreaks involved STEC O26, 1 involved STEC O145 and 1 involved STEC O103 (Table 5). There were 2 deaths (both in England) and 21 HUS cases (of which 19 were in England) reported to be associated with STEC outbreaks in 2024. A suspected or confirmed vehicle was identified for 3 of the 5 outbreaks. One was identified through analytical epidemiological studies or pathogen detection in a food isolate, while 2 had a lower level of certainty, as it was suspected following descriptive epidemiological analysis of questionnaire data (Table 5).

Table 5. STEC O157 and non-O157 foodborne national outbreaks in England, 2024

Outbreak agent	Total number of laboratory confirmed cases	Source of outbreak or vehicle of infection
STEC O26 t5.2323 stx2a, eae positive	56 (of which 54 cases in England)	Suspected beef product (note 1)
STEC O26 t5.2373 stx2a, eae positive	61 (of which 53 cases in England)	Suspected fresh fruit (note 1)
STEC O26 t5.2796 stx2a, eae positive	14 (of which 13 cases in England)	Not identified
STEC O103 t5.1948 stx1a, stx2a, eae positive	43 (of which 32 cases in England)	Not identified
STEC O145 t5.206 stx2a, eae positive	293 (of which 196 cases in England)	Confirmed salad leaves (note 2)

Note 1: Identified through epidemiological analysis of food exposure data only

Note 2: Identified through analytical epidemiological studies, food isolates testing or food chain investigations

STEC O26 outbreaks

Three national STEC O26 outbreaks were investigated in 2024.

UKHSA and public health agencies in devolved administrations (DAs) investigated an outbreak of STEC O26 stx2a, eae positive. There were 56 confirmed cases, of which 54 were resident in England. The median age was 5.5 years. ESQs containing clinical and exposure information were available for 96.4% (54) of cases. Overall, 64.3% (36) of cases reported bloody stools, 19 cases (33.9%) were hospitalised and 8 cases (14.3%) developed HUS; no deaths were reported. Epidemiological and food chain investigations identified a beef product to be the likely vehicle of infection.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O26 stx2a, eae positive. There were 61 confirmed cases, of which 53 resided in England. Questionnaires were received for 98.4% (60) of cases. The median age was 4 years. Twenty cases (32.8%) reported bloody diarrhoea and 9 (14.8%) cases reported hospitalisation for their symptoms; there were no reports of HUS or deaths. Epidemiological and food chain investigations suspected a fresh fruit as the likely vehicle of infection.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O26 stx2a, eae positive, consisting of 14 confirmed cases, of which 13 were resident in England. Cases had a median age of 7 years and ESQs were available for 92.9% (13), of which 64.3% (9) of cases reported bloody stools. Eight (57.1%) cases were hospitalised and 2 (14.3%) developed HUS; there were no reported deaths. The vehicle of infection was not identified.

STEC O145 outbreaks

One national STEC O145 outbreak was investigated in 2024.

UKHSA and public health agencies in DAs investigated an outbreak of STEC O145 stx2a, eae positive. There were 293 confirmed cases associated with the outbreak (196 in England). The median age was 29 years. ESQs were completed for 74.1% (217) of cases; bloody stools were reported by 72.4% (212) of cases. A total of 126 (43.0%) cases were hospitalised, 11 (3.8%) cases developed HUS and 2 cases died. Epidemiological (descriptive and analytical) and food chain investigations identified salad leaves as the confirmed vehicle of infection (13, 14). 

Other STEC non-O157 outbreaks

UKHSA and public health agencies in DAs investigated a national outbreak of STEC O103 stx1a, stx2a, eae positive, consisting of 43 confirmed cases (32 in England). The median age was 22 years. Questionnaires were available for 83.7% (36) of cases. Overall, 67.4% (29) of cases reported bloody stools and 34.9% (15) of cases were hospitalised; there were no reports of HUS or any deaths associated with this outbreak. The vehicle of infection was not identified.

Conclusions

The number of STEC case notifications to national surveillance continued to increase into 2024, driven by non-O157 STEC. Between 2015 and 2021, the number of O157 confirmed cases had been following a decreasing trend. However, case numbers have increased in recent years – although, notably, the rate was inflated in 2022 due to the largest O157 outbreak since the start of routine WGS. Whilst the number of O157 STEC notifications increased slightly from 2023 to 2024, they remain comparable to pre-pandemic rates in 2019. An increase in travel-related STEC O157 cases has also been observed since 2022. The percentage of cases reporting travel abroad during their incubation period is now exceeding pre-pandemic proportions from 2018 and 2019.

The STEC O157 seasonality displayed a rounded pattern in 2024, with a steady increase in the early summer and decline into winter. The non-O157 STEC seasonality displayed 2 distinctive peaks in 2024: one in April and May, attributable to a large outbreak during this time period, and another in September at the usual time period. Non-O157 STEC rates continued to display an increase earlier in the year and remained at a high rate in the winter months, compared to O157.

The age-sex distribution of O157 infections was similar to 2023, where the highest incidence was in the 1 to 4 years age group. The percentage of STEC O157 cases who developed HUS remained similar at 2.1%, as did the percentage of cases hospitalised for their illness (approximately 30%) compared to 2023, 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 2023, the most common non-O157 serogroup detected in 2024 was STEC O26 and cases infected with this serogroup had a higher proportion (8.4%) of HUS than O157 cases (2.1%).

The trends in the 2024 report continue to demonstrate the increase of non-O157 STEC. While trends are impacted by 5 outbreaks, increases in testing methods in the regions will increase STEC detection and therefore rates. Reassuringly, the rate of HUS remains less than 3% in both STEC non-O157 and O157 despite majority of the outbreak strains carrying the virulence factors stx2a and eae. 

Salad leaves, fresh produce and beef continue to be an important source of STEC outbreaks and specific interventions targeting these food products are important to prevent further outbreaks. Non-O157 STEC outbreaks pose a unique challenge due to nascent cross-sectoral awareness, for example, the infrequent non-O157 testing by food industries. Working with multidisciplinary partners under a One Health approach to investigate outbreaks of STEC, particularly non-O157, is vital to mitigate their impact on public health.

Appendices

Appendix 1. Confirmed STEC cases with co-infections

Serotype 1	Serotype 2	Stx profiles | eae | CC	Cases
O10:H4	O128:H2	stx2b, eae negative, CC25 stx2b, eae negative, CC10	1
O100:H30	O146:H21	stx2g, eae negative, CC10 stx1c, eae negative, CC442	1
O103:H2	O71:H8	stx1a, stx2c, eae positive, CC21 stx1a, eae positive, CC17	1
O103:H2	O157:H7	stx1a, eae positive, CC17 stx2a, stx2c, eae positive, CC11	1
O11:H43	O171:H21	stx1c, eae negative, no CC stx2d, eae negative, CC155	1
O113:H21	O8:H10	stx2d, eae negative, CC155 stx2d, eae negative, no CC	1
O114:H4	O145:H28	stx1c, eae negative, no CC stx2a, eae positive, CC32	1
O114:H4	O157:H7	stx1c, eae negative, no CC stx2c, eae positive, CC11	1
O123:H2	O157:H7	stx1a, eae positive, CC17 stx2c, eae positive, CC11	1
O126:H20	O176:H4	stx1a, stx2a,stx2d, eae negative, no CC stx1c, eae negative, no CC	1
O128:H2	O157:H7	stx1c, stx2b, eae negative, CC25 stx1a, stx2c, eae positive, CC11	1
O128:H2	O187:H52	stx1c, stx2b, eae negative, CC25 stx1c, eae negative, CC278	1
O128:H2	O21:H2	stx1c, stx2b, eae negative, CC25 stx1c, stx2b, eae negative, CC25	1
O145:H28	O26:H11	stx1a, eae positive, CC32 stx1a, eae positive, CC21	1
O146:H21	O166:H28	stx2b, eae negative, ST738 stx1c, stx2b, eae negative, no CC	1
O146:H21	O157:H7	stx1c, stx2b, eae negative, CC442 stx2a, eae positive, CC11	1
O146:H28	O157:H7	stx2b, eae negative, ST738 stx2c, eae positive, CC11	1
O153-O178:H7	O153:H7	stx1c, stx2b, eae negative, CC278 stx1c, stx2b, eae negative, CC278	1
O157:H7	O26:H11	stx2c, eae positive, CC11 stx2a, eae positive, CC21 (1)	6
O157:H7	O26:H11	stx1a, stx2c, eae positive, CC11 stx1a, eae positive, CC21 (1)	6
O157:H7	O26:H11	No stx, eae positive, CC11 stx2a, eae positive, CC21 (2)	6
O157:H7	O26:H11	stx1a, stx2c, eae positive, CC11 stx1a, eae positive, CC21 (1)	6
O157:H7	O26:H11	stx2a, stx2c, eae positive, CC11 stx2a, eae positive, CC21 (1)	6
O157:H7	O91:H4	stx2a, eae positive, CC11 stx1a, stx2b, eae negative, CC33	1
O174:H8	O45:H2	stx1c, eae negative, no CC stx2a, eae positive, CC165	1
O26:H11	O91:H14	stx2a, eae positive, CC21 stx1a, stx2b, eae negative, CC33	1
O38:H26	O91:H14	stx1c, eae negative, CC10 stx1a, stx2b, eae negative, CC33	1
O71:H8	O92:H33	stx1a, stx2a, eae positive, no CC No stx, eae positive, CC10	1
O76:H19	O91:H14	stx1c, eae negative, CC675 stx1a, stx2b, eae negative, CC33	1

Appendix 2. Prevalence of stx subtype combination reported amongst the top 10 non-O157 STEC serogroups in England, 2024

Serogroup (total number of cases)	Stx subtype	Number of cases	Percentage of cases
O103 (97)	stx1a	61	63
	stx1a;stx2a	33	34
	stx2a	2	2
	stx2c	1	1
O111 (37)	stx1a	30	81
	stx1a;stx2a	5	14
	stx1a;stx2c	1	3
	stx2a	1	3
O117 (61)	stx1a	59	97
	stx1a;stx2b	1	2
	stx2b	1	2
O128 (115)	stx1a	2	2
	stx1c	10	9
	stx1c;stx2b	79	68
	stx1c;stx2d;stx2b	1	1
	stx2b	23	20
O145 (247)	stx1a	2	1
	stx2a	243	98
	stx2c	1	0
	stx2f	1	0
O146 (227)	stx1a	1	0
	stx1c	73	32
	stx1c;stx2b	76	33
	stx1c;stx2d	2	1
	stx1c;stx2d;stx2b	1	0
	stx2a;stx1c	1	0
	stx2b	71	31
	stx2b;stx2d	2	1
O26 (356)	None	1	0
	stx1a	91	26
	stx1a;stx1c	1	0
	stx1a;stx2a	97	27
	stx2a	165	46
	stx2c	1	0
O76 (57)	stx1a;stx2a	1	2
	stx1c	40	70
	stx1c;stx2b	11	19
	stx1c;stx2d	1	2
	stx2a	4	7
O78 (38)	stx1c	32	84
	stx1c;stx2b	4	11
	stx2b	1	3
	stx2f	1	3
O91 (159)	stx1a	7	4
	stx1a;stx1c;stx2b	1	1
	stx1a;stx2b	131	82
	stx1c;stx2b	2	1
	stx2b	18	11

UKHSA STEC publications in 2024

1. Quinn O, Yanshi, King G, Hoban A, Sawyer C, Douglas A, Painset A, Charlett A, Nelson A, Rees C, Byers C, Williams C, Brown C, Mohan K, Brown C, Jenkins C, Neill C, Leckenby G, Larkin L, Allison L, Olufon O, Nickbakhsh S, Mannes T, Inns T, Balasegaram S. ‘National outbreak of Shiga toxin-producing Escherichia coli O145:H28 associated with pre-packed sandwiches, United Kingdom, May-June 2024’ Epidemiology and Infection 2024: volume 152, e179

2. Anthony C, Pearson K, Callaby R, Allison L, Jenkins C, Smith-Palmer A, James M. ‘Reasons for difficulties in isolating the causative organism during food-borne outbreak investigations using STEC as a model pathogen: a systematic review, 2000 to 2019’ Eurosurveillance 2024: volume 29, issue 49, 2400193

3. Poh CJ, Rodwell EV, Godbole G, Jenkins C. ‘Genotypic analysis of Shiga toxin-producing Escherichia coli clonal complex 17 in England and Wales, 2014-2022’ Journal of Medical Microbiology 2024: volume 73, issue 11, 001928

4. 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

5. Vusirikala A, Yanshi, Robin C, Rowell S, Dabke G, Fox G, Bell J, Manuel R, Jenkins C, Love NK, McCarthy N, Sumilo D, Balasegaram S. ‘Facilitators and barriers to implementing successful exclusion among children with shiga toxin-producing Escherichia coli: a qualitative analysis of public health case management records’ BMC Public Health 2024: volume 24, issue 1, page 2,272

6. Kesby M, Jorgensen F, Willis C, Aird H, Lai S, Sadler-Reeves L, Jenkins C, Chattaway M. ‘The microbiological quality of flour products in the UK with respect to Salmonella and Shiga-toxin-producing Escherichia coli’ Journal of Applied Microbiology 2024: volume 135, issue 7

7. 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

8. Greig DR, Do Nascimento V, Gally DL, Gharbia SE, Dallman TJ, Jenkins C. ‘Re-analysis of an outbreak of Shiga toxin-producing Escherichia coli O157:H7 associated with raw drinking milk using Nanopore sequencing’ Scientific Reports 2024: volume 14, issue 1, page 5,821

9. Vusirikala A, Rowell S, Dabke G, Fox G, Bell J, Manuel R, Jenkins C, Love N, McCarthy N, Sumilo D, Balasegaram S. ‘Shedding and exclusion from childcare in children with Shiga toxin-producing Escherichia coli, 2018-2022’ Epidemiology and Infection 2024: volume 152, e42

10. Rodwell EV, Greig DR, Godbole G, Jenkins C. ‘Clinical and public health implications of increasing notifications of LEE-negative Shiga toxin-producing Escherichia coli in England, 2014-2022’ Journal of Medical Microbiology 2024: volume 73, issue 2

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 that 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

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2. 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

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9. 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

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

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13. Quinn O, Yanshi, King G, Hoban A, Sawyer C, Douglas A, Painset A, Charlett A, Nelson A, Rees C, Byers C, Williams C, Brown C, Mohan K, Brown C, Jenkins C, Neill C, Leckenby G, Larkin L, Allison L, Olufon O, Nickbakhsh S, Mannes T, Inns T, Balasegaram S. ‘National outbreak of Shiga toxin-producing Escherichia coli O145:H28 associated with pre-packed sandwiches, United Kingdom, May-June 2024’ Epidemiology and Infection 2024: volume 152, e179

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