Scientists have reported a substantial increase in non-O157 Shiga toxin-producing E. coli (STEC) infections in England in recent years.
A study assessed how trends have been affected by factors such as increased use of PCR at hospital laboratory level. Audits in 2022 and 2023 identified 40 of about 100 labs reporting the PCR results for STEC.
Demographic, microbiological and clinical characteristics of non-O157 STEC from laboratory surveillance data from 2016 to 2023 in England were analyzed.
There was an almost 10-fold increase in diagnoses of non-O157 STEC from 2016 to 2023, according to the study published in the Journal of Medical Microbiology. This compares with an overall decreasing trend in notifications of STEC O157:H7 cases.
Most common E. coli types
A total of 9,378 isolates of non-O157 STEC were detected, including 338 different serotypes, and were linked to 9,311 individuals. Of these, 3,076 patients had a PCR-positive fecal specimen but STEC could not be isolated with culture methods. A total of 67 people had more than one strain of non-O157 STEC detected in their fecal specimen.
With the exception of 2020, the number of cases of non-O157 STEC has increased year on year from 297 in 2016 to 2,341 in 2023. The decrease in 2020 is attributed to measures to control the Covid pandemic.
A higher proportion of non-O157 STEC cases were female and aged between 20 and 39. International travel in the seven days before symptom onset was reported by 692 patients.
The most common serotypes were O26:H11, O146:H21, O91:H14, O128:H2, O145:H28, and O103:H2. STEC O26:H11 was more frequently reported in patients younger than 5 than any other age group, while the other main serotypes were more frequently isolated from adults. Cases of all six serotypes have risen since 2016, with STEC O145:H28 showing the biggest increase.
Shiga toxin (Stx) 2a, which has been associated with greater disease severity, was detected in 18 percent of patients. Where clinical details were available, 840 people were admitted to hospitals and 173 developed hemolytic uremic syndrome (HUS), a type of kidney disease.
Serotypes isolated from the nine fatal cases were O26:H11 three times, O55:H7 twice, and O91:H14, O145:H28, O183:H18, and O54:H45 all once.
Cases of STEC O145:H28 reported a higher rate of hospitalization than other non-O157 STEC cases. The serotypes most likely to be associated with HUS were O26:H11 and O145:H28. STEC harboring stx2f, stx2a, and stx2d were most frequently isolated from cases with HUS.
“Over the last decade, notifications of cases infected with non-O157 STEC in England have increased. We concluded that this trend is due partly to a more widespread use of the PCR approach at the local hospital level in England, but also represents a true increase in the clinical and public health burden of non-O157 STEC,” said researchers.
Hybrid strains analysis
Another study, published in the same journal, has assessed the public health concern of hybrid strains of Diarrheagenic E. coli (DEC).
In August 2022, UK Health Security Agency (UKHSA) surveillance detected an outbreak of Shiga toxin-producing E. coli/enterotoxigenic E. coli (STEC–ETEC) serotype O101:H33 harboring both Shiga toxin and heat-stable toxin. Nine people were sick but the source was not found.
There were 162 STEC–ETEC strains isolated between 2014 and 2023, of which 117 were human clinical isolates and 45 were of food or animal origin. The most common sequence types were ST329 and ST200, and the most frequently detected serotype was O187:H28.
The majority of clinical isolates were from females and adults. Food samples included raw milk, flour, hard cheese made from raw milk, and sprouts.
Travel history was recorded for 19 of 53 STEC-ETEC O1O1:H33 cases, of which 15 reported traveling outside the UK before getting sick and some isolates were multi-drug resistant.
“While notifications of hybrid strains of STEC–ETEC in the UK remain relatively low compared with other DEC pathotypes, this study provided evidence that foodborne outbreaks can occur,” said scientists.
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