It is unclear how excessively high levels of the additive were in the tortillas that made more than 700 people sick in Finland.
In August 2023, 721 people suffered from gastrointestinal symptoms in 17 schools in a Finnish municipality. Of these, 323 people’s symptoms quickly disappeared during lunch or within 30 minutes after eating.
A study published in the journal Eurosurveillance found that three samples of tortillas produced during a limited production period measured concentrations of the preservative calcium propionate at more than 24,000 mg/kg, exceeding the regulatory maximum limit of 2,000 mg/kg.
Researchers measured calcium concentrations in tortillas packaged within 9 minutes in the afternoon were nine times higher than products packaged later that day from the same lot. Analysis of calcium propionate in three high-calcium samples revealed 10-fold higher concentrations compared to two tortilla samples produced later.
The manufacturer has not identified a cause in the production process that could explain the high concentrations of calcium propionate, which can be used in bakery products to inhibit mold and extend shelf life.
Rapid onset of symptoms
Finland has a school lunch program that provides a free lunch every day to all students from kindergarten to high school. In many municipalities, meals are prepared in a central kitchen and distributed to satellite kitchens in schools.
In a questionnaire-based retrospective cohort study, consumption of flour tortillas and vegetable fillings served at lunch was statistically associated with illness. Of the 721 people, 683 were students. Five out of nine tortilla samples had a vinegar-like odor.
In August 2023, officials in the municipality of Mikkeli, eastern Finland, received information from the central kitchen that 10 to 20 students complained of vomiting and nausea 10 minutes after lunch in five of the municipality’s 19 schools.
An online survey was created and more than 100 people reported gastrointestinal symptoms. The Finnish Institute for Health and Welfare (THL) and the Finnish Food Agency (Ruokavirasto) have also joined the outbreak investigation.
The most common symptoms were abdominal pain, nausea, and headache, followed by diarrhea, vomiting, and muscle pain. 58 people showed symptoms during lunch, and 265 people showed symptoms within 30 minutes after lunch. The average disease duration was 4 to 12 hours. The sick person did not visit a health care provider.
Of the total, 167 said their tortillas tasted bad or strange, 24 said they had a bad or strange smell, and 130 said their food tasted like soap or detergent.
Hazards from chemicals
Tortillas were packaged in modified atmospheres, 18 per package, opened in the school kitchen, and served unheated according to the manufacturer’s instructions. Guests filled their own tortillas.
The tortillas served at the 16 schools consisted of two batch numbers with the same expiration date. Manufacturing and delivery to Finland involved Poland and the Netherlands. It has been distributed to multiple sites, including community feeding providers, but no gastrointestinal illnesses have been reported.
Inspections of the central kitchen and field and satellite kitchens revealed no hygiene violations that could explain the outbreak.
In three tortilla samples, the concentrations of calcium propionate and propionic acid exceeded the maximum allowable levels. Samples with higher concentrations were from tortillas packaged between 13:24 and 13:32.
Suspicion over the tortillas was later limited to one batch and packaging time range (13:12 to 16:33), but the operator discarded both batches.
“Our findings remind us that chemicals are the cause of foodborne outbreaks and the need for increased surveillance in Europe. Schools should be better prepared for sudden foodborne outbreaks and there should be guidelines for discontinuing school meals for safety reasons,” the scientists said.
