Researchers have found a significant increasing trend for sporadic E. coli O26 and E. coli O80 HUS cases during a decade in France but a notable decrease for E. coli O157.

E. coli–associated hemolytic uremic syndrome (HUS) is a substantial public health risk in France, according to scientists. HUS is a severe complication associated with E. coli infections that causes kidney failure and can lead to brain damage and other lifelong complications.

Researchers conducted a study of 1,255 sporadic pediatric cases reported from 2012 to 2021, and findings were published in the journal Emerging Infectious Diseases.

Annual case notifications ranged from 109 in 2014-15 to 163 in 2017. Most were in children younger than three years of age. E. coli serogroups O26, O80, and O157 accounted for 78 percent of cases, and 13 significant clusters were identified.

Sporadic cases recorded
In France, Shiga toxin-producing E. coli (STEC) surveillance is through voluntary clinical and microbiological surveillance of HUS in children younger than 15. Annual incidence rates for pediatric STEC-HUS are relatively high. Cases of suspected STEC-HUS in those under 15 are reported to Santé Publique France, the country’s public health agency.

Microbiological STEC surveillance is voluntary and coordinated by the National Reference Center (CNR) for E. coli, Salmonella, and Shigella at Institut Pasteur and its associated laboratory. 

Determining the source of contamination for sporadic cases is difficult for reasons including limited epidemiologic data, multiple potential sources of contamination, and gaps in knowledge about pathogen source–pathway interactions, said scientists.

A sample was sent to CNR for 1,132 cases, and 717 had an STEC serogroup identified. The top-3 serogroups accounted for 559 of 717 cases: O26 with 228 cases, O80 with 149, and O157 with 182 cases.

The proportion of female and male patients was comparable over the study period. Almost 800 of the 1,255 cases were in patients younger than three years of age. Incidence rates varied by age group, with the largest in children 1 to 2 years old. The highest incidence occurred from July to October.

For STEC O26 and STEC O80, regions in the eastern half of France had slightly higher incidence rates. For STEC O157, the top rates were primarily in northwest France.

Clusters found
Scanning by serogroup identified two significant clusters: STEC O26 in 2019 in southeast France and STEC O80 in 2017 in northeast France. WGS data for the isolates within the 2019 O26 cluster identified three WGS-linked clusters of two isolates each. However, epidemiological investigations did not identify a common source of infection.

Southeast France is the country’s second most densely populated region and includes a major city, Lyon, but also rural areas and high cattle density.

Annual scanning identified 13 significant clusters. There was at least one cluster each year, except for 2014 and 2017, with a maximum of three in 2018. The median cluster size was 10 cases but ranged from two to 20 cases. Clusters occurred from June to November, and most corresponded to the seasonal peak seen in STEC-HUS notifications from July to October.

“The results of this study have numerous implications for outbreak detection and investigation and research perspectives to improve knowledge of environmental risk factors associated with geographic disparities in STEC-HUS in France,” said researchers.

“Taking into account geographic differences is relevant to the analysis of surveillance data for outbreak detection purposes, particularly for evaluating epidemiologic signals and deciding to initiate investigations. We plan to use our results in further studies to explore the association with environmental parameters potentially underlying STEC-HUS risk in France.” 

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