Shiga toxin-producing Escherichia coli (STEC) data: 2019 - ISS-G20 Laboratorium Repository

Main points for 2019

The main points of the 2019 report are:

1. A total of 539 confirmed cases of Shiga toxin-producing Echerichia coli (STEC) O157 were reported in England and Wales in 2019.

2. The lowest incidence of STEC O157 was in the East Midlands region (0.56 per 100,000 population) and the highest in the Yorkshire and Humber region (1.51 per 100,000 population).

3. Children aged 1 to 4 years had the highest incidence of infection (3.28 per 100,000 population, CI 95% 2.63–4.04).

4. Nearly one-third of confirmed STEC O157 cases in England were hospitalised and 3% were reported to have developed haemolytic ureamic syndrome (HUS).

5. In England and Wales, detection of non-O157 STEC increased in line with the growing number of NHS labs implementing gastrointestinal (GI) diagnostics using polymerase chain reaction (PCR); in 2019, 768 culture-positive non-O157 STEC cases (655 in England, 113 in Wales) were reported.

6. A further 347 specimens in England and 66 in Wales were positive for Shiga toxins (stx) genes on PCR at the Gastrointestinal Bacteria Reference Unit (GBRU) but an organism was not cultured.

7. The most commonly isolated non-O157 STEC serogroup was STEC O26 (England: n=109/655, 17% and Wales: n=28/113, 25%).

8. Five outbreaks of STEC involving 65 cases in England were investigated in 2019.

Background

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 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 to 4).

The most common serogroup of STEC causing illness in England is O157 (5). Other serogroups (termed non-O157) can also cause illness and have been implicated in outbreaks in England and elsewhere.

Frontline laboratories in England use culture methods to detect STEC O157 by its inability to ferment sorbitol on selective media (MacConkey agar). However, non-O157 STEC ferment sorbitol and there is no culture method to differentiate non-O157 STEC from non-pathogenic E.coli in frontline laboratories. Therefore, detection of non-O157 STEC relies on PCR.

The implementation and roll-out of a GI PCR at frontline hospital laboratories began in December 2013, and to December 2019 around 20% of frontline laboratories were using it. As a consequence, there has been a substantial increase in the detection of non-O157 cases. However, PCR is not universally used for detection of non-O157 STEC, and the true incidence remains unknown.

While non-O157 STEC can cause serious illness, variation exists among non-O157 STEC serogroups in their associations with severe disease, likely explained by differences in the virulence factors produced by different strains. STEC can produce 2 Shiga toxins (Stx), Stx1 (of which there are 4 subtypes 1a–1d) and/or Stx2 (of which there are 7 subtypes stx2a–2g).

The presence of Stx2, specifically subtype stx2a, is more likely to cause HUS (1), (6). The increasing numbers 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 and risk group of the patient and potential pathogenicity of the strain of STEC infecting the patient, is challenging. In response, new Interim Public Health Operational Guidance for STEC for the public health management of O157 and non-O157 STEC cases (including an algorithm to assist in follow-up decision making) was published by the STEC Guidelines Update Working Group in August 2018.

National enhanced surveillance of STEC in England and Wales has been undertaken since 2009. This report summarises the epidemiological data on confirmed cases of STEC O157 and non-O157 STEC cases in England in 2019 and compares it to previous years.

Methods

The National Enhanced Surveillance System for STEC (NESSS) infection in England began in January 2009 in order 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, in order to improve outbreak recognition and facilitate public health investigations. The data is collected from enhanced surveillance questionnaires (ESQs) 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 the UK Health Security Agency Health Protection Teams (UKHSA HPTs) and then refer samples to the GBRU for confirmation and further testing. Each HPT arranges for the ESQ to be completed for all cases to obtain a detailed history for the 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.

Data included in this report was validated and extracted from NESSS and cases meeting the case definitions below were included in analyses. Laboratory data for cases in Wales was extracted and validated from the UKHSA Gastro Data Warehouse (GDW). Welsh data is included in Figure 1 as only laboratory data was available and is excluded from other sections of the report.

Data from the 2019 Office for National Statistics (ONS) mid-year population estimates was 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.

Entire content available on: https://www.gov.uk/government/publications/escherichia-coli-e-coli-o157-annual-totals