Research and analysis

Shiga toxin-producing Escherichia coli (STEC) data: 2022

Updated 15 May 2025

The main points of the 2022 annual report are:

Overall, 2,063 cultured-confirmed cases of Shiga toxin-producing Escherichia coli (STEC) were reported in England during 2022, an increase of 79.2% compared to 2021.

A total of 762 culture-confirmed cases of STEC O157 were reported in England in 2022, more than double the number reported in 2021 (up 108.8%) and an increase of 48.0% compared with 2019. A total of 1,998 cases of STEC non-O157 were reported in England in 2022 (including 1,301 culture-confirmed cases and 697 faecal specimens positive for stx genes on PCR but culture-negative), an increase of 61.9% compared to 2021 and of 94.0% compared to 2019. Among culture-confirmed non-O157 cases, the most commonly isolated serogroup was STEC O26 (n=186/1301, 14.3%).

Children aged 1 to 4 years had the highest annual incidence of infection due to STEC O157 (3.48 per 100,000 population, 95% confidence interval (CI) 2.78 to 4.30). Children aged under 1 year had the highest incidence of infection due to STEC non-O157 (13.25 per 100,000 population, CI 10.49 to 16.51).

Where information was available, around a third (30.9%, 223 out of 722) of confirmed STEC O157 cases in England were hospitalised and 1.8% (13 out of 722) were reported to have developed Haemolytic Uraemic Syndrome (HUS). Where information is available, one third (29.3%, n=176/600) of STEC non-O157 cases in England were hospitalised; and 1.6% (32 out of 1998) of STEC non-O157 were reported to have developed HUS. 3 deaths were reported among STEC O157 cases, and 3 deaths among STEC non-O157 cases.

Four outbreaks of STEC involving 299 cases, 235 of whom were resident in England were investigated in 2022. Two outbreaks involved STEC O157, 1 involved STEC O103 and 1 involved STEC O145. Suspected vehicles were identified for all 4 outbreaks and included beef, salad leaves, 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.

Frontline 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 20% 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.

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) and/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 2022 and compares this data to previous years.

COVID-19 pandemic

During 2020 and 2021 it is likely that the emergence of SARS-CoV-2 (COVID-19) and subsequent non-pharmaceutical interventions (NPIs) implemented to control COVID-19 transmission affected notifications of STEC infections to national surveillance in several ways. These include, but are not limited to, changes which may have impacted ascertainment (such as healthcare seeking behaviour, access to health care, availability, or capacity of testing) as well as changes which likely impacted incidence (such as closures of educational settings, limited foreign travel, closure of hospitality and attractions such as petting farms) which will have also varied over time. Therefore, trends presented in this report should be interpreted with caution.

Additional in-depth analyses examining the impact of the COVID-19 pandemic are underway which will be published separately.

Methods

The National Enhanced Surveillance System for STEC (NESSS) infection in England began in January 2009 to provide a rapid review of common exposures 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 Public Health (Control of Diseases) Act 1984 and 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
• 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 2022 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 case(s)
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 2022

In 2022, 2,063 culture-confirmed cases of STEC were reported in England, an increase of 79.2% compared to 2021. These comprised 762 culture-confirmed cases of STEC serogroup O157 and 1,301 cases where a serogroup other than O157 was isolated (non-O157). For a further 697 cases, faecal specimens were confirmed as STEC by testing positive by PCR for stx genes, but STEC could not be detected on culture.

Twenty-six confirmed cases were infected with multiple serogroups. The most commonly reported serogroups in a co-infection were O157 (n=7), O146 (n=6) and O26 (n=5) (Appendix 1).

O157 STEC cases in England

The crude incidence rate of confirmed STEC O157 in England in 2022 was 1.33 per 100,000 population (95% CI 1.30 to 1.50), an increase compared to 2021 and higher than pre-pandemic levels. This is highest rate observed in the last 9 years, discontinuing the downward trend observed since 2015 (Figure 1) (8). A large outbreak of STEC O157 with 195 cases who were resident in England  has contributed to the increase in 2022, but these cases do not solely account for the increase.

The rates in 2020 and 2021 were the lowest rates reported annually since 1996, when testing began in England for STEC O157 on all faecal specimens from patients with suspected gastrointestinal infection (9). However, it is likely that the COVID-19 pandemic contributed to the reduced rates so this trend should be interpreted with caution.

Figure 1. Incidence of Shiga toxin-producing Escherichia coli (STEC) O157 culture-confirmed cases by year, England, 2013 to 2022

Figure 2. Incidence of STEC O157 in England by region, 2022 only

The highest incidence of STEC O157 was in the North East (2.46 cases per 100,000 population, 95% CI 1.90 to 3.13) and the lowest was in the London (0.79 cases per 100,000 population, 95% CI 0.62 to 1.00) (Figure 2).

Age, gender and seasonality of STEC O157 cases

Of 762 confirmed STEC O157 cases in England, 417 (54.7%) were female. In 2022, children aged 1 to 4 years had the highest incidence of infection (3.48 per 100,000 population, CI 2.78 to 4.30)(Figure 3).

Figure 3. Age-sex specific incidence rate of STEC O157 cases in England, 2022

STEC O157 infections in England display a distinct seasonality with the peak of infection in the summer months, July or August. However, in 2022 infections peaked in September due to a large UK-wide outbreak (Figure 4). 

Figure 4. Seasonal trend of laboratory confirmed cases of STEC O157 in England, 2015 to 2022

Severity of illness

While number of STEC O157 cases has fluctuated since 2015, the proportion of cases completing an ESQ has remained above 90% (Figure 5). Of the 762 confirmed STEC O157 cases in England in 2022, ESQs were received for 724 (95.0%) (Figure 5). Of those, 722 (94.8%) were fully completed STEC ESQs and symptoms were reported for 715 (99.0%) cases; the majority of which reported diarrhoea (94.6%, n=683) as well as bloody stools (57.8%, n=417). Other symptoms included abdominal pain (611, 84.6%), nausea (342, 47.4%), vomiting (369, 33.0%), and fever (340, 30.5%). Hospitalisation was reported by 30.9% (n=223) of cases; duration of hospitalisation ranged from 1 to 24 days with median stay of 3 days. There were 3 deaths reported among cases of O157 STEC (all were adults).

During 2022, HUS occurred in 13 confirmed cases (1.8%), nearly two-thirds of which were under 5 years of age (n=8, 62%), with a median age of 3 years (range 1 to 60 years old). The incidence of STEC O157 HUS in children under 5 years in 2022 was 0.26 per 100,000 cases per population (CI 0.11 to 0.51).

Figure 5. The number of confirmed STEC O157 cases and percentage of enhanced surveillance questionnaires received in England, 2022

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 (10). 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
• beef

In England, of the 722 confirmed cases for whom ESQs were received during 2022, there were 696 primary or co-primary cases, 19 secondary cases, and 7 asymptomatic contacts. A decrease in travel related cases was observed with 127 cases (17.6%) reporting travel abroad during their incubation period (7 days prior to onset), compared to 28% and 31% in 2018 and 2019 respectively but an increase compared to 2020 and 2021 when COVID-19 restrictions impacted international travel (8% and 4% respectively). Of those 127, only 35 spent their entire incubation period abroad.

Frequently reported subtypes of STEC O157

In September 2022, phage typing for STEC samples at GBRU was discontinued. As such phage typing data below is only representative of January to September. As with previous years, phage type (PT) 8 and PT21/28 were the most commonly reported STEC O157 phage types in 2022 (Figure 6) along with PT14 – they had a combined proportion of 45.9%. These were followed by PT1 (7.3%), PT54 (6.5%), PT4 (6.2%) and PT32 (5.9%). The peak in PT34 in 2016 was due to a large outbreak linked to mixed-salad leaves, where 165 cases were reported between 31 May and 29 July 2016 (4).

Figure 6. Percentage of STEC O157 cases by the 10 of the most common phage types, 2015 to 2022 [note 1]

Note 1: data for 2022 is reported for only January to September.

Among 762 isolates from confirmed STEC O157 cases in England in 2022, most (n=403, 53%) had stx1+2, 46.9% (n=357) had stx2 only, and 0.3% (n=2) had stx1 only. Of those isolates with stx2 or stx1+2, 33.9% (n=258) had stx2a; the subtype most likely to cause severe clinical presentation and HUS.

Non-O157 STEC cases in England

Historically, cases of non-O157 STEC have been under ascertained, with 89 cases of STEC non-O157 reported between 2009 and 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.

During 2022 in England, faecal specimens from 6,509 human cases were received at GBRU for STEC testing. Among those, there were 1,301 culture-confirmed STEC non-O157 specimens, and a further 697 were PCR positive but STEC could not be cultured. It is estimated that most stx PCR positive, but culture negative specimens, correspond to STEC non-O157, leading to an estimated total of 1,988 STEC non-O157 cases in England in 2022, an increase of 62% compared to 2021. This number was above pre-pandemic levels, with an increase of 94.0% compared to 2019. Of 1,301 culture-positive STEC non-O157 cases, 90 different serogroups were confirmed by WGS. For 23 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 1,301 culture-confirmed cases in 2022 were O26 (n=186, 14.3%) followed by O146 (n=166, 12.8%), O91 (n=133, 10.2%), O103 (n=101, 7.8%) and O128ab (n=84, 6.5%) (Appendix 2). Four were also in the top 5 non-O157 serogroups reported in 2021 (Shiga toxin-producing Escherichia coli (STEC) data: 2021).

In 2022, ESQs were received for 31% (n=625/1,998) of non-O157 STEC cases, of which 39% (n=511/1,301) were for culture positive non-O157 STEC cases, and 15% 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 (Figure 7). 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 27% in 2019 the percentage of non-O157 cases for which an ESQ was received has increased to 35% in 2021. However, this increase should be interpreted with caution due to the impacts of the COVID-19 pandemic during this period, which likely resulted in fewer notifications and therefore a reduced burden of cases requiring follow up.  

Figure 7. The number of STEC non-O157 cases and percentage of enhanced surveillance questionnaires received in England, 2022

Of 1,998 STEC non-O157 cases in England, 1,177 (59%) were female. In 2022, children aged under 1 had the highest incidence of infection (13.25 per 100,000 population, CI 10.49 to 16.51) (Figure 8).

Figure 8. Age-sex specific incidence rate of STEC non-O157 cases in England, 2022

STEC non-O157 infections in England in 2022 displayed a distinct seasonality with the peak of infection in the late summer and autumn months, July to October (Figure 9) with a second peak in November. This is later than the typically observed O157 seasonal trend which usually peaks in during the summer months.

Figure 9. Seasonal trend of laboratory confirmed cases of non-O157 STEC in England, 2015 to 2022

Information on symptoms was available for 618 non-O157 STEC cases. Of these 618 ESQs, 600 (97%) cases were symptomatic. Among the symptomatic cases, 86.2% (n=517) reported diarrhoea, including bloody stools in 52.8% (n=317) cases. This was accompanied by abdominal pain (n=402, 67.0%), nausea (n=226, 37.7%), vomiting (n=181, 30.2%) and fever (n=166, 27.7%). In total 176 cases (29.3%) were hospitalised.

HUS occurred in 1.6% (32/1,998) of STEC non-O157 cases. From these 32 cases, the most frequently isolated serogroups were O26 (34.4%, n=11) and O145 and O121 (6.3%, n=2 each). Serogroup was unavailable for 10 cases (31.3%), 9 of which were culture negative and 1 where the O group was unidentifiable. 11% of confirmed STEC O26 cases developed HUS as compared to 2% in confirmed STEC O157 cases. HUS cases ranged from 9 months to 75 years of age and 31.3% (n=10) were between 1 and 4 years of age. There were 3 deaths reported among cases of non-O157 STEC (2 adults and 1 child).

Among all 1,998 isolates from non-O157 STEC cases in England in 2022, 43.6% (n=872) possessed the stx1 toxin alone, 30.5% (n=610) possessed stx1+2 and 25.8% (n=516) possessed stx2 toxin alone (Figure 10, Appendix 2). The most common stx subtypes detected through sequencing of the 1,301 isolates were:

• stx1a only in 26.1% (n=340)
• stx1c only in 15.4% (n=210)
• stx1c stx2b in 15.1% (n=196)
• stx2a only in 11.6% (n=151)
• stx2b only in 9.1% (n=119)
• stx1a stx2b in 8.1% (n=106)
• stx1a stx2a in 5.5% (n=72)

The following were reported in approximately 1% of isolates (Figure 10, Appendix 2):

• stx2a stx2e(n=15)
• stx2g only (n=15)
• stx2e only (n=12)
• stx2d (n=8)
• stx2c (n=7)

An additional 17 stx subtype combinations were detected in the samples of 31 cases. Of the 1,998 isolates, 773 (38.7%) had the eae gene.

Figure 10. Prevalence of stx subtype combinations reported among the top 9 non-O157 STEC serogroups in England, 2022

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 2022 (Figure 11). While the notifications of STEC O157 have declined the number of STEC non-O157 has increased two-fold (211.4%) 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 particular drivers (11).

Figure 11. Percentage of laboratory confirmed STEC cases in England by serogroup, 2015 to 2022

STEC O26 cases in England

Questionnaires were received for 94.6% (n=176) of all 186 confirmed STEC O26 cases. Of the 170 (69.6%) cases that were symptomatic, 95.3% (n=162) cases had diarrhoea, 62.4% (n=106) reported abdominal pain, 44.1% (n=79) reported bloody stools, 36.5% (n=85) vomiting, and 32.9% (n=73) nausea. Overall, in 2022 a lower proportion of STEC O26 cases (28.2%, n=48) were hospitalised compared to STEC O157 cases (30.9%, n=223), while a higher proportion of HUS was reported in O26 cases with 6.5% (n=11) compared to 1.8% in O157 cases (n=13).

Of 186 STEC O26 cases in England, 113 (60.8%) were female. Children aged 1 to 4 years of age comprised 36.0% (n=67) of cases (Figure 12).

Figure 12. Age-sex specific incidence rate of STEC O26 cases in England, 2022

STEC O145 cases in England

Questionnaires were received for 81.7% (n=49) of all 60 confirmed STEC O145 cases. Of the 46 (93.6%) cases that were symptomatic, 91.3% (n=42) cases had diarrhoea, 78.3% (n=36) reported abdominal pain, 32.6% (n=15) vomiting, 76.1% (n=35) bloody stools and 34.8% (n=16) nausea. Overall, in 2022 a higher proportion of STEC O145 cases (45.7%, n=21) were hospitalised compared to STEC O157 cases 30.9% (n=223), while a higher proportion of HUS was reported in O145 cases with 4.3% (n=2) compared to 1.8% in O157 cases (n=13).

Of 60 STEC O145 cases in England, 37 (61.7%) were female. Children aged 1 to 4 years of age comprised 16.7% (n=10) of cases (Figure 13).

Figure 13. Age-sex specific incidence rate of STEC O145 cases in England, 2022

STEC O103 cases in England

Questionnaires were received for 45.5% (n=46) of all 101 confirmed STEC O103 cases. Of the 46 (100.0%) cases that were symptomatic, 91.3% (n=42) cases had diarrhoea, 71.7% (n=33) reported abdominal pain, 23.9% (n=17) vomiting, 63.0% (n=29) bloody stools and 37.0% (n=17) nausea. Overall, in 2022 a lower proportion of STEC O103 cases (19.6%, n=9) were hospitalised compared to STEC O157 cases 30.9% (n=223), and no O103 cases progressed to HUS compared to 1.8% in O157 cases (n=13).

Of 101 STEC O103 cases in England, 55 (54.5%) were female. The age group with the highest proportion of cases were older among O103 cases compared to O157, O26 and O145, with children aged 10 to 19 years of age comprising 21.8% (n=22) of cases (Figure 14).

Figure 14. Age-sex specific incidence rate of STEC O103 cases in England, 2022

Outbreaks

STEC outbreaks investigated in England during 2022

Four STEC outbreaks affecting 299 people, 235 of whom were resident in England, were investigated in 2022. Typically, an exceedance is investigated when 5 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.

Two outbreaks were caused by O157 and therefore accounted for 27.7% of confirmed STEC O157 cases. The other 2 outbreaks were caused by O103 and O145. The O103 outbreak accounted for 0.8% of non-O157 cases and 9.9% of O103 cases. The O145 outbreak accounted for 0.8% of non-O157 cases and 16.7% of O145 cases (Table 2).

There was 1 death and no HUS cases associated with outbreaks in 2022.

Suspected vehicles were identified for all four outbreaks. Three were identified through analytical studies or pathogen detection in a food isolate, while the fourth had a lower level of certainty, as it was suspected based solely on questionnaire data (Table 2).

Table 2. STEC O157 and non-O157 outbreaks in England, 2022

Agent	Total number affected	Total laboratory confirmed	Hospitalised	Source	Setting
STEC O157 stx2a stx2c	18	17 [note 1]	9	Foodborne (suspected, beef product)	National
STEC O157 stx2a	259	259 [note 2]	55	Foodborne (suspected, salad leaves [note 4])	National
STEC O103 stx1a	12	12 [note 3]	1	Foodborne (suspected, soft cheese [note 4])	National
STEC O145 stx2a	10	10	3	Foodborne (suspected, pasteurised milk [note 4], [note 5])	Regional

Notes to Table 2

Note 1: 15 confirmed cases in England, 1 in Scotland and 1 in Wales.

Note 2: 195 confirmed cases in England, 18 in Northern Ireland, 33 in Scotland and 13 in Wales.

Note 3: 10 confirmed cases in England and 2 in Wales.

Note 4: identified through analytical studies or pathogen detection in a food isolate.

Note 5: post pasteurisation contamination of pasteurised milk, most likely due to contaminated milk bottles that were insufficiently sterilised, and subsequent failure to maintain the cold chain.

---

In August, UKHSA, with Public Health Scotland (PHS) and Public Health Wales (PHW), investigated an outbreak of STEC O157 stx2a stx2c eae positive. There were 17 confirmed cases and 1 possible case of which, 15 completed an ESQ; 73% of cases reported bloody stools (n=11), 67% were admitted to hospital (n=10). One case was reported to have developed HUS and one case associated with this cluster died, although it is unknown whether their STEC infection was causal or contributory to their death. Descriptive epidemiological investigations identified beef as the most highly reported product (80%), specifically beef burgers (67%). A food isolate, from diced beef, also fell within the same 5-SNP cluster as the cases.

In September 2022, UKHSA along with Public Health Agency of Northern Ireland (PHA NI), PHS and PHW investigated an outbreak of STEC O157 stx2a eae positive. There were 259 confirmed cases, of which 195 were resident in England, 18 in Northern Ireland, 33 in Scotland and 13 in Wales. The median age was 29 years. Full ESQs, containing clinical and exposure information, were available for 98% of cases (n=254). Overall, 65% of cases reported blood in stools (n=165) and 75 were hospitalised (30%) but none developed HUS. No deaths were reported. Epidemiological investigations identified salad leaves as the likely vehicle of infection (12).

UKHSA and PHW investigated an outbreak of STEC O103 stx1a eae positive in August 2022. There were 12 confirmed cases of which 10 cases resided in England and 2 in Wales. Questionnaires were received for 11 (92%) cases. Nine cases reported bloody diarrhoea (83%) and 1 reported hospitalisation for their symptoms (8%); there were no reports of HUS or deaths. Epidemiological investigations identified soft cheese as the likely vehicle of infection (13).

In August 2022, UKHSA investigated an outbreak of STEC O145 stx2a eae positive. There were 10 cases associated with the outbreak, all of which were laboratory confirmed at the 5-SNP level. All 10 cases were resident in England. The median age was 70 years. ESQs were completed for 9 of the 10 confirmed cases (90.0%). Overall, 50.0% of cases reported blood in stools (n=5) and 3 were hospitalised (30.0%). There were no reports of HUS or deaths in association with this outbreak. Although epidemiological investigations were undertaken no vehicle of infection was identified for all cases, though a post pasteurisation contamination of milk was the likely vehicle for some cases (14).

Conclusions

The number of STEC case notifications to national surveillance increased in 2022, driven by both an increase in O157 and a continued rise in non-O157 cases.

In recent years the number of O157 confirmed cases has been on a downward trajectory; in 2022 the number of O157 cases in England increased to the rates reported pre-2015. Though there was a large O157 outbreak with 195 confirmed cases resident in England, this does not solely account for the observed increase. While the number of cases is around double that of 2021, the measures implemented during the COVID-19 pandemic could have affected the transmission of STEC also; this is supported by the data presented in this report – the number of cases minus the large national outbreak, is consistent with the numbers of cases reported in pre-COVID years. An increase in outbreaks caused by O157 was observed in 2022, with 2 out of the 4 outbreaks.

This report presents changes in the epidemiology of STEC O157 infections in 2022; a peak in reporting in the summer months aligned with previous years but a second larger later peak was observed in the autumn months, which was mostly driven by a large national outbreak. The age-sex distribution returned to patterns observed in pre-pandemic years with the highest incidence in the 1 to 4 year old age group and an overall higher incidence in females. While the percentage of STEC O157 cases who developed HUS remained similar at 1.8%, the percentage of cases hospitalised for their illness decreased in 2022 compared to 2021 (36.0% and 30.9% respectively) returning to similar levels from pre-pandemic years (for example, 29% in 2019), suggesting better ascertainment of more clinically severe cases during 2020 and 2021 which is supported by studies on the impact of COVID-19 on GI pathogen surveillance.

The detection of non-O157 STEC infections increased compared to 2021, continuing the trend observed in pre-COVID-19 years. The most common non-O157 serogroup detected in 2022 was STEC O26 and cases infected with this serogroup had a higher proportion (6.5%) of HUS than O157 cases (1.8%). Half of the outbreaks in 2022 were caused by non-O157 serogroups.

Overall trends during 2022 should be interpreted with caution due to the changes in STEC testing, a large national outbreak and the remaining wide-ranging impacts of the COVID-19 pandemic. It is likely that the interventions implemented to control COVID-19 in 2020 and 2021 led to a reduction of STEC transmission for both O157 and non-O157 infections. However, given the decreasing trend in pre-COVID-19 years, it is unlikely that the increase in STEC cases in 2022 can be wholly attributed to the removal of COVID-19 control measures alone.

Appendices

Appendix 1: Confirmed cases with co-infections

Case	Serogroup 1	Serogroup 2	Serogroup 3 (where applicable)
1	O26:H11	O125ac:H6
2	O63:H6	O156:H8
3	O157:H7	O177:H11
4	O128ab:H2	O63:H6
5	O177:H11	O157:H7
6	O91:H14	O146:H21
7	O145:H28	O15:H18
8	O46:H31	O134:H31
9	O182:H25	O109:H16
10	O111:H8	O26:H11
11	O91:H14	O146:H21
12	O8:H9	O181:H16
13	O26:H11	O181:H16
14	O8:H9	O38:H26
15	O91:H14	O146:H21	O157:H7
16	O146:H21	O76:H19
17	O145:H28	O26:H11
18	O182:H25	O157:H7
19	O91:H14	O128ab:H2
20	O111:H8	O157:H7
21	O166:H15	O123:H2
22	O157:H7	O177:H11
23	O157:H39	O146:H21
24	O146:H21	O unidentifiable:H7
25	O98:H21	O unidentifiable:H20
26	O unidentifiable:H21	O26:H11

Appendix 2: Prevalence of stx subtype combination reported among the top 9 non-O157 STEC serogroups in England, 2022

Serogroup	stx subtype	n	%
O26 (n=186)	stx1a	80	43.0%
	stx2a	52	28.0%
	stx1a stx2a	52	28.0%
O146 (n=166)	stx1c	63	38.0%
	stx1c stx2b	60	36.1%
	stx2b	37	22.3%
	stx1c stx2d	3	1.8%
	stx1c stx2d stx2b	2	1.2%
	stx1a stx2c	1	0.6%
O91 (n=133)	stx1a stx2b	105	78.9%
	stx2b	20	15.0%
	stx1a	5	3.8%
	stx1a stx1c stx2b	1	0.8%
	stx1c stx2b	1	0.8%
	stx2d	1	0.8%
O103 (n=101)	stx1a	97	96.0%
	stx2a	4	4.0%
O128AB (n=84)	stx1c stx2b	57	67.9%
	stx2b	23	27.4%
	stx1c	2	2.4%
	stx1c stx2d stx2b	1	1.2%
O145 (n=60)	stx2a	55	91.7%
	stx2f	3	5.0%
	stx2a stx2c	1	1.7%
	stx2c	1	1.7%
O117 (n=56)	stx1a	51	91.1%
	stx1c	2	3.6%
	stx1a stx2b	1	1.8%
	stx1a stx1c	1	1.8%
	stx2b	1	1.8%
O76 (n=36)	stx1c	28	77.8%
	stx1c stx2b	5	13.9%
	stx1c stx2c	1	2.8%
	stx1c stx2d	1	2.8%
	stx2a	1	2.8%
O113 (n=35)	stx1c stx2b	31	81.6%
	stx2a	3	7.9%
	stx2d	2	5.3%
	stx1c stx2d stx2b	1	2.6%
	stx2b	1	2.6%

UKHSA STEC publications in 2022

1. Jenkins C, Bird PK, Wensley A, Wilkinson J, Aird H, Mackintosh A, Greig DR, Simpson A, Byrne L, Wilkinson R, Godbole G, Arunachalam N, Hughes GJ; Incident Management Team. ‘Outbreak of STEC O157:H7 linked to a milk pasteurisation failure at a dairy farm in England, 2019’. Epidemiology and Infection 2022 May 18, volume 150, e114

2. 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 August, volume 71, issue 8

3. Dallman TJ, Jalava K, Verlander NQ, Gally D, Jenkins C, Godbole G, Gharbia S. ‘Identification of domestic reservoirs and common exposures in an emerging lineage of Shiga toxin-producing Escherichia coli O157:H7 in England: a genomic epidemiological analysis’.The Lancet Microbe 2022 August, volume 3, issue 8, pages e606 to e615

4. 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 February 11, volume 150, e52

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 and Food Safety (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 January 29, volume 6, issue 1, e009933

2. Dodd CC, Cooper MJ. ‘Multidisciplinary response to the Escherichia coli O104 outbreak in Europe’ Military Medicine 2012 November, volume 177, issue 11, pages 1406 to 1410

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 October 31, volume 18, issue 44, article 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 May, volume 23, issue 18, article 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 October, volume 26, issue 10, pages 2394 to 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 July, volume 70, issue 7, article 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 August 11, volume 15, article 324

8. Butt S, Jenkins C, Godbole G, Byrne L. ‘The epidemiology of Shiga toxin-producing Escherichia coli serogroup O157 in England, 2009–201’ Epidemiology and Infection 2022 February 11, volume 150, e52

9. Adams NL, Byrne L, Smith GA, Elson R, Harris JP, Salmon R, Smith R, O’Brien SJ, Adak GK, Jenkins C. ‘Shiga Toxin-Producing Escherichia coli O157, England and Wales, 1983–2012’ Emerging Infectious Diseases 2016 April, volume 22, issue 4, pages 590 to 597

10. Dallman TJ, Jalava K, Verlander NQ, Gally D, Jenkins C, Godbole G, Gharbia S. ‘Identification of domestic reservoirs and common exposures in an emerging lineage of Shiga toxin-producing Escherichia coli O157:H7 in England: a genomic epidemiological analysis’ The Lancet Microbe 2022 August, volume 3, issue 8, pages e606 to e615

11. 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 August, volume 71, issue 8

12. 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 September, volume 29, issue 36, article 2400161

13. Heinsbroek E, Blakey E, Simpson A, Verlander NQ, Greig DR, Jorgensen F, Nelson A, Douglas A, Balasegaram S, Jenkins C, Elson R. ‘An outbreak of Shiga toxin-producing Escherichia coli serotype O103:H2 associated with unpasteurized soft cheese, England and Wales, 2022’ Epidemiology & Infection 2025 January 22, volume 152, e172

14. Jenkins C, Bird PK, Wensley A, Wilkinson J, Aird H, Mackintosh A, Greig DR, Simpson A, Byrne L, Wilkinson R, Godbole G, Arunachalam N, Hughes GJ and others; Incident Management Team. ‘Outbreak of STEC O157:H7 linked to a milk pasteurisation failure at a dairy farm in England, 2019’ Epidemiology and Infection 2022 May 18, volume 150, e114