An increase in a type of E. coli over the past decade has prompted scientists to warn of an emerging threat to public health in England.

While part of the rise is because of better detection of non-O157 Shiga toxin-producing E. coli (STEC) in labs, there is evidence more people are actually getting sick.

Researchers looked at STEC O26:H11 clonal complex (CC) 29 in England. Between January 2014 and December 2021, 834 human isolates from 724 patients belonging to CC29 were sequenced at the UK Health Security Agency (UKHSA).

STEC O26:H11 notifications in 2021 were eight times higher than those recorded in 2014. Diagnoses of STEC O26 in England have increased each year from 19 in 2014 to 144 in 2021. Most cases were female and the highest proportion belonged to the 0 to 5 age group, found the study in the Journal of Infection.

Hemolytic Uremic Syndrome (HUS) was diagnosed in 40 cases and three children died. HUS is a severe complication associated with E. coli infections that causes kidney failure.

Continued rise in reports
STEC O157:H7 has been the dominant serotype in the UK with public health surveillance systems focused on detecting and monitoring it. However, changing lab methods have improved the detection of all STEC serotypes.

Diagnoses of infection caused by CC29 increased every year except for 2020. Seasonality of STEC O26:H11 follows similar patterns to O157, wher cases rise in the summer months, peak in August and decrease to baseline levels during winter.

The most common serotype was O26:H11, followed by O111:H8, and O177:H11. The remaining isolates were 16 different types. Most isolates belonged to sequence type (ST) 21, ST29, and ST16.

South East England reported the most STEC cases belonging to CC29, followed by London.

Of 40 patients that developed HUS, 21 were male. Most cases were aged 5 or under. The number increased from two cases in 2014 to 11 in 2021.

For CC29, 133 of 680 cases reported travel outside the UK in the seven days before the onset of symptoms. The most common destinations were Egypt, Turkey, Morocco, and Mexico.

Recorded outbreaks
Outbreaks of O26:H11 in England before 2020 included six travel-related clusters and one linked to salad in prepacked sandwiches. From January 2020 to December 2021, another six clusters with three or more cases were found.

The two largest had 16 cases over 14 months and 11 cases over 44 months. There was epidemiological evidence implicating salad as a potential vehicle of infection, but this was not /confirm/ied. Another outbreak was linked to a petting farm and the source was unknown for the others.

Data showed STEC O26:H11, which had a type of Shiga toxin known as stx1a, leads to severe clinical outcomes, as over half reported bloody diarrhea with a quarter being hospitalized. Guidance was updated in July 2021 to include public health follow-up on all cases of STEC O26:H11, regardless of stx profile.

“Determining the true incidence and prevalence is challenging due to inconsistent national surveillance strategies. Improved diagnostics and surveillance algorithms are required to monitor the true burden, detect outbreaks and to implement effective interventions,” said researchers.