Research and analysis

HPR volume 17 issue 15: news (20, 21 and 28 December 2023)

Updated 28 December 2023

Outbreak of Shiga toxin-producing E. coli (STEC) O145 and unseasonably high reporting of non-O157 STEC infections in the UK, December 2023

The UK Health Security Agency (UKHSA), Public Health Scotland (PHS), Food Standards Agency (FSA) and Food Standards Scotland (FSS) are working together with other partner agencies to investigate an outbreak of Shiga toxin-producing Escherichia coli (STEC) O145 identified through the analysis of whole genome sequencing (WGS) data.

STEC is often transmitted via consumption of contaminated food but can also be spread by close contact with an infected person, as well as direct contact with an infected animal (usually ruminants) or its environment. The symptoms of STEC infection can vary in severity, ranging from mild diarrhoea to severe abdominal cramps, vomiting and bloody diarrhoea. In up to 15% of cases, infection can lead to the development of haemolytic uraemic syndrome (HUS), a serious and life-threatening condition predominantly affecting the kidneys, which can result in death (1). HUS is most often seen in young children (under 5 years) but can also affect other vulnerable groups, including the elderly and immunocompromised. The O145 outbreak strain currently under investigation possess a virulence gene (stx2a) which is associated with a more severe clinical presentation and progression to HUS.

As of 27 December 2023, 30 confirmed cases have been reported across England and Scotland since late July 2023, with most cases reported in December 2023. Fifteen cases are female (50%), with ages of all cases ranging from 7 to 81 years (median age of 35 years). For those with information available (n=19), 63% (n=12) have reported bloody diarrhoea, 58% (n=11) reported hospitalisation for their illness and 1 case developed HUS. One death has been associated with this outbreak. Epidemiological and food chain investigations have identified links between some of the identified cases and a number of unpasteurised cheeses produced by a business in England.

As a precautionary measure, the FSA issued a product recall on 24 December 2023 for 4 cheeses. A further product was recalled on 27 December. UKHSA is continuing to follow up cases to identify any common links, including determining whether cases ate or came into contact with the recalled cheeses.

In addition to the above outbreak, UKHSA has also been working with partner agencies to investigate 3 other non-O157 STEC outbreaks across the UK since October 2023. These outbreaks have also been identified through WGS and include a different strain of STEC O145 and 2 outbreaks of STEC O26. The number of cases associated with these outbreaks varies from 15 to 44 reported cases.    

Historically, STEC O157 was the most commonly identified type of STEC in England and Wales, with around 600 cases reported each year. Most cases of STEC (O157 and non-O157) are usually reported in summer and early autumn (2). During October and November, the number of non-O157 STEC cases notified to UKHSA was over double the median reported number compared to previous years, excluding the COVID-19 pandemic years (2017 to 2019 annual mean of 618 cases versus 1,372 cases reported in 2023). While detection of non-O157 STEC has increased in recent years following the implementation of molecular detection methods in frontline laboratories, this level of reporting has not been seen before at this time of year and thus cannot be wholly attributed to the adoption of molecular-based technology and UKHSA together with partner agencies are investigating this increase.

The driver of the general increase in non-O157 STEC case reporting has not yet been identified. However, analysis of the available information from questionnaires completed by cases, and the national distribution of cases, suggest that these identified outbreaks are all likely foodborne in origin and involve a variety of different sources. Investigations remain ongoing to identify the sources of contamination and implement risk management and public health protection actions.

References

1. Byrne L, Adams N, Jenkins C (2020). ‘Association between Shiga toxin-producing Escherichia coli O157:H7 Stx gene subtype and disease severity, England, 2009 to 2019’ Emerging Infectious Diseases: volume 26, issue 10, pages 2,394 to 2,400

2. UKHSA. ‘Shiga toxin-producing Escherichia coli (STEC) data: 2020’

Increase in extensively-drug resistant Shigella sonnei in England predominantly affecting men who have sex with men

There has been an increase in Shigella cases reported in England between January 2022 and November 2023, during which period there has also been an increase in the proportion of extensively-drug resistant (XDR) Shigella spp. The recent increase in XDR Shigella spp. from June 2023 onwards has been driven by one specific cluster of Shigella sonnei.

Shigella spp. are bacterial enteric pathogens transmitted through faecal-oral contact that cause acute bacillary dysentery. In England, while Shigella infection is a common cause of travellers’ diarrhoea and transmission can be foodborne, it is increasingly associated with sexual contact among gay, bisexual, and other men who have sex with men (GBMSM). Antimicrobial resistance among Shigella spp. is a public health concern, with the World Health Organization listing Shigella as an antimicrobial resistant ‘priority pathogen’ (1).

As of 18 December 2023, the number of reported Shigella spp. cases in England has increased between January 2022 and November 2023 reaching a monthly peak of 485 in September 2023. There has also been an increase in the number of XDR Shigella spp., which peaked at 67 cases in June 2023 (Figure 1). This XDR increase has been driven by a single cluster of closely related Shigella sonnei (outbreak strain t10.1814). The number of cases within this cluster increased substantially in 2023, such that in 2023 (up to and including November) there were 97 cases within this cluster (Figure 2); 90% of cases are adult males with a median age of 35 years, which suggests a predominance of sexual transmission of this strain of Shigella among gay, bisexual, and other men who have sex with men (GBMSM).

Figure 1. Number of Shigella spp. diagnoses, England, January 2022 to November 2023, by XDR and non-XDR antimicrobial resistance profiles

Figure 2. Number of Shigella spp. diagnoses within Shigella sonnei cluster (t10.1814), England, January 2022 to November 2023

XDR is defined as non-susceptibility to at least one agent in all but 2 or fewer antimicrobial categories (2). This XDR strain displays high levels of genotypic resistance against macrolides (azithromycin), fluroquinolones, aminoglycosides, sulphonamide, trimethoprim and tetracycline. In addition, isolates show further resistance determinants including blaCTX-M-15 which is associated with extended spectrum β-lactamase production, the principal mechanism of resistance to cephalosporins. Standard treatment with first line agents like quinolones, azithromycin and ceftriaxone will not be effective. Isolates within this cluster are sensitive to carbapenems and chloramphenicol.

Previous outbreaks with XDR Shigella sonnei in GBMSM have shown cases have a higher rate of complications (up to 25%) and hospitalisation (3). While most cases are likely to get self-limiting gastroenteritis, those who are GBMSM, in extremes of age, or those with underlying co-morbidities, are at a higher risk of complications and will need antibiotics for management.

Antibiotic treatment is recommended in cases with severe symptoms, those requiring hospital admission, those with prolonged diarrhoea (beyond 7 days) or who have underlying immunodeficiency. Oral treatment options are limited to antibiotics such as chloramphenicol, pivmecillinam and fosfomycin. Use of either pivmecillinam or fosfomycin would be off label or unlicensed; they should only be considered for treating uncomplicated cases such as prolonged diarrhoea. Due to a lack of evidence of their efficacy in severe infections, mecillinam and fosfomycin should not be used in the immunocompromised or cases with sepsis or severe colitis; consideration should be given to intravenous carbapenems (ertapenem or meropenem) or oral chloramphenicol.

References

1. WHO (2017). ‘Prioritization of pathogens to guide discover, research and development of new antibiotics for drug-resistant bacterial infection’

2. Magiorakos AP, and others (2012). ‘Multidrug-resistant, extensively drug-resistant and pandrug-resistant bacteria: an international expert proposal for interim standard definitions for acquired resistance’ Clinical Microbiology and Infection: volume 18, number 3, pages 268 to 281

3. Charles H, and others (2022). ‘Outbreak of sexually transmitted, extensively drug-resistant Shigella sonnei in the UK, 2021 to 2022: a descriptive epidemiological study’ Lancet Infectious Diseases: volume 22 number 10, pages 1,503 to 1,510

SSI in NHS hospitals in England: annual report in summary

The latest annual report summarising data submitted to the national Surgical Site Infection Surveillance Service by 183 NHS hospitals and 8 independent sector NHS treatment centres in England has been published. The annual report presents SSI risk benchmarks for each of 17 surgical categories, trends in SSI incidence and variation among participating hospitals. It also includes risk-stratified SSI incidence including, for the first time, SSI risk by ethnicity and Index of Multiple Deprivation.

Surveillance data for 125,095 procedures and 1,222 surgical site infections (SSI) detected during inpatient stay or on readmission to hospital was submitted in financial year 2022 to 2023 (1). Compared to the previous financial year (2021 to 2022), the number of procedures submitted increased by 8.4%. However, the number of operations remained 7% lower than pre-pandemic (2019 to 2020).

NHS trusts performing surgery in any of 4 orthopaedic categories (hip replacement, knee replacement, reduction of long bone fracture and repair of neck of femur) are required to undertake surveillance of SSI for a minimum of one 3-month surveillance period per financial year.

Trust-level SSI risk results for mandatory orthopaedic categories can be found as accompanying supplementary tables (2).

Key findings include:

• 10-year trends in the annual inpatient and readmission SSI risk varied by surgical category with 8 seeing marginal increases from the previous year
• the SSI risk for hip replacement procedures due to fracture decreased: from 2.5% in 2021 to 2022 to 0.7% in 2022 to 2023
• the SSI risk in hip and knee replacement was higher for patients residing in the most deprived areas of the country; the white ethnic group was overwhelmingly the most commonly reported ethnic group across all surgical categories, varying between 73% and 98.9%
• given the small operation volumes in other ethnic groups, the comparisons between SSI risks were challenging to obtain reliably; however, there was some suggestion that SSI risk was slightly elevated among Black patients undergoing reduction of long bone fracture
• among SSIs with accompanying microbiology data, Enterobacterales continued to make up the largest proportion of isolates for both superficial SSI (32.6%) and deep or organ and space SSI (26.8%)
• the highest proportion of organ or space infections were in large bowel surgery (38.8%)
• 9 trusts were identified as high outliers for the mandatory surveillance categories (3 in hip replacement, 2 in knee replacement, 1 in reduction of long bone fracture and 3 in repair of neck of femur) in 2022 to 2023
• in 2022 to 2023, 2 eligible trusts did not meet the mandatory participation surveillance requirements, compared to 3 Trusts in the previous year

References

1. UKHSA (December 2023). ‘Surveillance of surgical site infections in NHS Hospitals in England, April 2022 to March 2023’

2. UKHSA (December 2023). ‘Surgical site infections surveillance: NHS trust tables April 2021 to March 2023’

Third UK One Health report

The third UK One Health Report has been published on GOV.UK and is the product of a continuing cross-government initiative bringing together data on the levels of antibiotic use in humans and animals. It presents data on resistance to antibiotics, including high priority antibiotics, in bacteria that are common to both humans and animals in the UK, as well as comparative data on antimicrobial resistance (AMR) in isolates from retail meat.

The report finds that the total combined quantity of antibiotics used in human and veterinary medicine dropped by 28% between 2014 and 2019. The levels of resistance dropped or remained stable between 2014 and 2019 for the majority of antibiotics tested in bacterial isolates from healthy food-producing animals.

Other highlights include:

• key outcome indicators on antibiotic use and resistance presented in the report show the progress made in reducing antibiotic use and resistance in both veterinary and human medicine; the majority of indicators have reduced or remained stable between 2014 and 2019
• in 2019, approximately one third of all UK antibiotic medicines were used in animals and two-thirds in humans; the use of antibiotics per bodyweight was 103mg/kg in humans compared to 30mg/kg in food-producing animals
• similar patterns of AMR are seen in Campylobacter species found in chickens, chicken meat and people which suggests strong linkages through the food chain; this contrasts with AMR trends in Salmonella spp. and E. coli which show much more variation and makes it less likely that resistance in these bacteria in animals is a key driver of AMR in people via the food chain
• some of the latest research in 2 emerging areas – AMR in the environment and in companion animals – was included, highlighting the importance of filling knowledge gaps to improve understanding of transmission routes

This year’s UK One Health report includes updates on governmental and stakeholder initiatives across the UK to contain and control AMR that were initiated between 2019 and 2023. Such initiatives take account of the 5-year National Action Plan on AMR and the UK’s 20-year vision for AMR. The vision sets out the ambition for AMR to be contained and controlled by 2040, covering human health, animal health, the environment and the food chain.

Updated typhoid and paratyphoid public health guidance

UKHSA’s public health guidance on typhoid and paratyphoid (enteric fever), including the related enhanced surveillance questionnaire, has recently been updated.

In summary, changes to the guidance are as follows:

• for cases with a positive clearance sample after one course of antibiotics, it is recommended that a subsequent clearance sample should be taken one week after the positive result – if subsequent sample is positive, then further sampling should be delayed at least by a week

• if samples are persistently positive (for example, after one month from first clearance sample), ensure household contacts have been screened and results are negative prior to further sampling of the case

• for non-travel related cases, all household and close contacts should be screened where an obvious source of illness cannot be identified

• if the case is without recent travel history and has possible carrier status, consider taking a follow-up sample (at least 6 weeks after the first antibiotic course) to assess carrier status, even if the case is not in a risk group (no exclusion is required for these cases unless they are symptomatic)

Main changes to the enhanced surveillance questionnaire (ESQ) are that:

• health protection teams are requested to record co-traveller status and risk group of cases and contacts in the ESQ
• there are more detailed questions on specific travel history and information about pre-travel health advice

The guidance, algorithms, enhanced surveillance questionnaire, additional trawling questionnaire, template letter for contacts, microbiological clearance form and typhoid factsheet are available at Typhoid and paratyphoid: public health guidance and questionnaires.

Technical briefings

Influenza A(H1N2)v: rapid technical assessment

Infection reports

Group A streptococcal infections: first update on seasonal activity in England, 2023 to 2024

Common animal-associated infections (England): third quarter 2023

Surveillance of surgical site infections in NHS hospitals in England: 2022 to 2023

Laboratory surveillance of paediatric bacterial bloodstream infections and antimicrobial resistance in England: 2018 to 2022

Vaccine coverage reports

Quarterly vaccination coverage statistics for children aged up to 5 years in the UK (COVER programme): July to September 2023