Nationwide outbreak of Shiga toxin-producing Escherichia coli infections associated with frozen pizzas, France, 2022.

In February 2022, we observed an increase in the number of paediatric patients with haemolytic uraemic syndrome (HUS) associated with Shiga toxin-producing Escherichia coli (STEC) in France. We interviewed cases or caretakers about food exposures, identified purchases on supermarket loyalty cards, conducted a case-control study, tested food samples and characterised isolates. We identified 59 cases of STEC O26:H11 or O103:H2 infections nationwide from 18 January to 5 April 2022. Fifty cases presented with HUS and two died. Data from supermarket loyalty cards identified frequent purchase of Brand A Type B frozen pizzas. A case-control study confirmed a strong association between the consumption of Brand A pizzas and illness (OR = 116.0; 95% confidence interval (CI): 26.8-501.9). Manufacturing of Brand A Type B pizzas did not include pre-baking of the dough. Isolates from pizza dough and flour samples were indistinguishable from the clinical outbreak strains. On 18 March, the manufacturer recalled the Type B pizzas. While flour is a known STEC vehicle, this outbreak is highly unusual, as cooking of frozen pizzas should eliminate STEC. Further research aiming to understand the origins and persistence of contamination should contribute to improving food safety practices.