Calcium propionate in tortillas – a likely cause of a large outbreak of acute gastrointestinal illness, Finland, 2023

In August 2023, 721 individuals became ill with gastrointestinal symptoms in 17 schools in a Finnish municipality. Of these, 323 (45%) developed quickly passing symptoms during school lunch or < 30 min after the lunch. In a questionnaire-based retrospective cohort study, consumption of flour tortillas and vegetable filling served at lunch were statistically associated with illness (adjusted odds ratio (aOR) = 3.3; 95% confidence interval (CI): 1.4-7.4 for the tortillas and aOR = 1.5; 95% CI: 1.1-2.1 for the filling). Abnormal odour was observed in five of nine tortilla samples. In three samples from tortillas produced during a limited production period, high concentrations of calcium propionate (E 282) were measured (> 24,000 mg/kg), exceeding the regulatory maximum limit of 2,000 mg/kg. The tortillas served at lunch were traced to a manufacturer in another EU country. The manufacturer was unable to identify any cause in the production process that could explain the high concentrations of calcium propionate. Our results are in line with findings from other investigations that excessive calcium propionate can induce gastrointestinal symptoms. The investigation highlights the need for strengthened surveillance of chemical-related food-borne outbreaks in Europe and timely communication between school staff and public health authorities to support rapid outbreak detection and response.