By Ana Espino | Published on April 1st, 2026 | 4 min read
Shiga toxin-producing
Escherichia coli (STEC) infections are the leading cause of hemolytic
uremic syndrome (HUS) in children. This severe complication combines hemolytic
anemia, thrombocytopenia, and acute kidney failure, and can sometimes be
life-threatening.
Despite
structured surveillance, identifying sources of contamination remains complex
due to the
diversity of foodborne vectors and the often unexpected nature of
exposures.
In 2022, an
unusual increase in pediatric HUS cases was observed in France, triggering a
large-scale national investigation. Identifying the source proved particularly
challenging in a context of multiple exposures and no obvious signal.
This study,
published in Eurosurveillance in 2026, aimed to provide an integrated
description of the epidemiological, microbiological, and traceability
investigations in order to identify the origin of the outbreak and draw
practical lessons for food safety.
Can a simple
pizza trigger an outbreak?
A total of
59
cases were identified between January and April 2022, including
50 pediatric
HUS cases and
2 deaths, highlighting the severity of the outbreak. The median
age was
6 years, with a predominance in northern France.
Epidemiological
analysis, combining
interviews, loyalty card data, and a case–control study,
revealed a strong association between illness and the consumption of frozen
pizzas from a specific brand. The case–control study showed a very high risk.
Traceability
investigations identified a single production facility responsible for
manufacturing these pizzas. A key feature was the absence of pre-baking of the
dough, which differs from usual industry standards.
Microbiological
analyses confirmed the presence of STEC O26:H11 and O103:H2 in pizza dough and
flour, with strains genetically identical to those found in patients.
Contamination
may have been facilitated by specific production conditions, particularly a
proofing phase at 35°C, favorable to bacterial growth. In addition, domestic
cooking may have been insufficient to eliminate the pathogen, especially due to
thick dough and uneven temperatures in some ovens.
Following the
product recall on 18 March 2022, a rapid decline in cases was observed,
confirming the causal role of the pizzas in the outbreak.
An
underestimated foodborne risk
STEC infections
represent a major public health concern, particularly in children due to the
risk of
severe HUS. This study sought to identify the origin of a
large
national outbreak and to clarify its transmission mechanisms.
The findings
highlight the role of an unexpected vehicle—
frozen pizzas with non-prebaked
dough—underscoring vulnerabilities in certain production chains and challenging
established
assumptions in food safety.
However, some
uncertainties remain, particularly regarding
bacterial survival despite cooking
and the precise stages of the initial contamination.
Although
further investigations are needed, these findings call for a reassessment of
industrial practices and consumer recommendations. Ultimately, they may
contribute to strengthening safety standards for flour-based products and
reducing the risk of similar outbreaks.
Read next: Viruses in our gut, a threat to the heart?
About the author – Ana Espino
PhD in Immunology, specialized in Virology
As a scientific writer, Ana is passionate about bridging the gap between research and real-world impact. With expertise in immunology, virology, oncology, and clinical studies, she makes complex science clear and accessible. Her mission: to accelerate knowledge sharing and empower evidence-based decisions through impactful communication.
