Rise in the number of notifications of Shiga toxin-producing Escherichia coli (STEC) infections probably linked to an increased use of multiplex PCR assays, Germany, 2023

BACKGROUNDShiga toxin-producing <i>Escherichia coli</i> (STEC) can cause illnesses ranging from self-limiting diarrhoea to severe manifestations such as haemolytic-uraemic syndrome (HUS). In 2023, an increase in notified STEC cases was observed in the German federal state of Lower Saxony and nationwide.AIMWe aimed to investigate possible reasons for the observed increase.METHODSWe analysed data on notified STEC cases at federal and state level. All available STEC isolates from Lower Saxony from 2023 were whole genome sequenced. We sent a survey on detection and identification methods to 25 clinical microbiology laboratories in Lower Saxony.RESULTSIn 2023, a statistically significant increase in notified STEC cases in all ages was seen in Lower Saxony and nationwide when compared with case numbers in 2022 and the median of 2015-2019 (p < 0.01). The highest increase was observed in people aged 60-69 years: 110 cases were notified in Lower Saxony in 2023 (median 2015-2019: 26) and 471 cases nationwide (median 2015-2019: 182). No overall increase was seen in disease severity or in the number of HUS cases. No larger genetic clusters or outbreaks were identified in Lower Saxony. The survey among the 17 responding laboratories in Lower Saxony revealed an increased use of multiplex PCR assays for gastrointestinal pathogens, introduced mainly in 2023.CONCLUSIONThe increase in notified STEC cases was probably associated with the implementation of multiplex PCR assays for the analysis of gastrointestinal specimens. Our findings highlight the need to monitor diagnostic practices when assessing and evaluating surveillance data.