# Shiga Toxin-Producing E. coli (STEC) from Danish Patients, 1997–2023: Diagnostic Trends and Bacteriological Findings

## TL;DR

This paper examines how changes in diagnostic methods for Shiga toxin-producing E. coli (STEC) in Denmark from 1997 to 2023 have increased detection rates and impacted clinical interpretation.

## Contribution

The study highlights the impact of molecular diagnostics and whole genome sequencing on STEC detection trends and clinical microbiology practices.

## Key findings

- The number of diagnosed STEC cases in Denmark increased from 31 in 1997 to 1432 in 2023.
- Whole genome sequencing revealed a wide spectrum of STEC types, including cross-over pathotypes.
- Subtypes stx2a and stx2d are associated with an increased risk of haemolytic uraemic syndrome (HUS).

## Abstract

Implementation of molecular detection methodology of Shiga toxin-producing Escherichia coli (STEC) in Danish patients began in 1997. Since then, changes in molecular detection methods and diagnostic criteria have led to the present situation, in which almost all diarrhoeal stool specimens are examined for STEC. Whole genome sequencing (WGS) of STEC isolates referred to the national reference laboratory has increased the detailed characterisation, and revealed a large spectrum, of STEC types, including cross-over pathotypes typically associated with extraintestinal disease or traveller’s diarrhoea. Association of subtype stx2a (and stx2d) with the risk of developing haemolytic uraemic syndrome (HUS) was confirmed. These changes have resulted in an increase in the number of diagnosed STEC cases from 31 cases in 1997 to 1432 in 2023. Similar increases in Europe have also been recorded. Culture of STEC is, on the other hand, declining, which poses a challenge to the identification of multiple STEC infections and outbreaks. Syndromic (PCR) test panels have also resulted in an increase in the detection of multiple microorganisms. Double or triple infections have increased the role of clinical microbiologists in interpreting and assessing the significance of diagnostic results and have also increased the need for high-quality curation of surveillance data.