It remains unclear how excessively high levels of an additive got into tortillas that made more than 700 people sick in Finland.
In August 2023, 721 individuals became ill with gastrointestinal symptoms in 17 schools in a Finnish municipality. Of these, 323 developed quickly passing symptoms during lunch or under 30 minutes after the meal.
In three samples from tortillas produced during a limited production period, concentrations of the preservative calcium propionate above 24,000 mg/kg were measured, exceeding the regulatory maximum limit of 2,000 mg/kg, according to a study published in the journal Eurosurveillance.
Researchers measured nine times higher concentrations of calcium in tortillas packed within nine minutes in the afternoon compared with products from the same lot and packaged later that day. Calcium propionate was analyzed in three samples with high calcium content, and 10 times higher concentrations were found compared with samples from two tortillas produced later.
The manufacturer did not identify a cause in the production process that could explain the high concentrations of calcium propionate, which can be used in bakery products to inhibit molds and prolong shelf life.
Rapid symptom onset
Finland has a school meal program, offering a daily free lunch to all students from preschool to upper secondary. 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 filling served at lunch were statistically associated with illness. Of the 721 cases, 683 were students. A vinegar-like odor was noted in five of nine tortilla samples.
In August 2023, officials in the city of Mikkeli in Eastern Finland received information from the central kitchen of 10 to 20 students falling ill with vomiting and nausea 10 minutes after having lunch at 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 Authority (Ruokavirasto) joined the outbreak investigation.
The most common symptoms were abdominal pain, nausea, and headache, followed by diarrhea, vomiting, and muscle pain. Fifty-eight cases developed symptoms during lunch and 265 less than 30 minutes after lunch. The median duration of illness was 4 to 12 hours. No sick people visited healthcare providers.
Of all cases, 167 mentioned a bad or strange tortilla taste, 24 a bad or strange odor, and 130 said that food tasted of soap or detergent.
Risk from chemical agents
Tortillas were delivered packaged in a modified atmosphere, 18 per package, opened in school kitchens and served unheated as instructed by the manufacturer. Diners filled the tortillas themselves.
Tortillas served at the 16 schools were of two batch numbers with the same best before date. Manufacture and shipping to Finland involved Poland and the Netherlands. They were distributed to several places, including providers of community meals, but no gastrointestinal illnesses were reported.
Inspections of the central kitchen and onsite and satellite kitchens did not reveal any hygiene breaches that could explain the outbreak.
In three tortilla samples, concentrations of calcium propionate and propionic acid exceeded the maximum permitted level. Samples with elevated concentrations were from tortillas packaged between 13:24 and 13:32.
Although the suspicion regarding tortillas was later limited to one batch and a packaging time window (13:12–16:33), the operator destroyed both batches.
“Our findings remind us of chemical agents as causes of foodborne outbreaks and the need for enhanced surveillance in Europe. Schools should be better prepared for sudden-onset foodborne outbreaks, and guidelines to interrupt school meals for safety reasons should exist,” said scientists.