# Shiga Toxin–Producing Escherichia coli Outbreak in Canadian Daycare Centers

## TL;DR

A large STEC outbreak in Canadian daycare centers led to significant healthcare use and showed that proactive monitoring can help prevent severe outcomes like HUS.

## Contribution

The study demonstrates the effectiveness of daily laboratory monitoring in predicting hemolytic uremic syndrome in STEC-infected children.

## Key findings

- 7.4% of infected children developed HUS, lower than typical outbreak rates.
- Daily TMA screening showed 100% sensitivity and 95.7% specificity for predicting HUS.
- Proactive monitoring and coordinated public health response reduced severe outcomes.

## Abstract

What were the health care resource utilization and clinical outcomes associated with a large single-source pediatric Shiga toxin–producing Escherichia coli (STEC) outbreak, beginning in Canadian daycare centers?

In this cohort study, 326 primary and 33 secondary infections were identified among 288 children and 71 adults; among the 285 children with available outcome data, there were 508 and 395 emergency department and STEC clinic visits, respectively. Overall, 40 children were hospitalized, 21 children developed hemolytic uremic syndrome (HUS), and 9 children required dialysis; daily laboratory monitoring identified all future HUS cases.

This cohort study found that significant health care resources were used to monitor, treat, and optimize outcomes in this large single-source STEC outbreak.

This cohort study describes health care resource utilization, clinical outcomes, and outcomes associated with daily laboratory monitoring for thrombotic microangiopathy in a large, single-source Shiga toxin–producing Escherichia coli outbreak in Canadian daycare centers.

Shiga toxin–producing Escherichia coli (STEC) infections have significant morbidity, with 15% to 20% of children developing hemolytic uremic syndrome (HUS), more than half of whom require kidney replacement therapy (KRT).

To describe health care resource utilization, clinical outcomes, and outcomes associated with daily laboratory monitoring for thrombotic microangiopathy (TMA) in a large point-source STEC outbreak.

This retrospective cohort study was conducted among a population-based cohort of individuals exposed to a contaminated food item served in 11 childcare centers in Calgary, Alberta, Canada, on August 29, 2023. Children and adults with confirmed STEC infection linked to the outbreak were included. Data were analyzed from June 9, 2025, to January 5, 2026.

E coli O157:H7 possessing genes encoding Shiga toxins 1 and 2.

Health care utilization, symptoms and signs of infection, occurrence of HUS and KRT, and results of TMA screening.

There were 359 outbreak-linked confirmed STEC infections, including 285 children (median [IQR] age, 3.3 [2.3-4.2] years; 141 [62.4%] male) and 71 adults (median [IQR] age, 38.8 [31.9-46.4] years; 58 [81.7%] female) and 3 out-of-province cases; 326 primary and 33 secondary infections were identified. Of 359 infected individuals overall, 66 (18.4%) were asymptomatic. HUS occurred in 21 children (7.4%), all of whom had diarrhea (21 of 206 children with diarrhea [10.2%]). No adults developed HUS. This outbreak was linked to 508 and 395 visits by children with STEC to an emergency department and a dedicated STEC clinic, respectively; 591 visits occurred during a 7-day period, starting 6 days after exposure. Forty children were hospitalized, 9 children required KRT, and 3 children required intensive care. The most common symptoms in children and adults were diarrhea (206 children [91.2%]; 16 of 20 adults with data [80.0%]), abdominal pain (141 children [62.4%]; 11 of 20 adults with data [55.0%]), and bloody diarrhea (127 children [56.2%]; 7 of 20 adults with data [35.0%]). TMA testing had 100% (95% CI, 83.9%-100%) sensitivity, 95.7% (95% CI, 92.0%-98.0%) specificity, and a diagnostic accuracy of 96.1% (95% CI, 92.7%-98.2%) for development of HUS.

This cohort study reporting on a point-source STEC outbreak identified significant use of health care resources. Only 7% of children infected with STEC developed HUS, which is lower than reported in most prior outbreaks and sporadic case series. These findings highlight the importance of a coordinated public health response integrated with clinical care and suggest that proactive screening for TMA has the potential to mitigate adverse outcomes.