High additive levels likely cause of large outbreak in Finland
It remains unclear how excessively high levels of an additive ended up in the tortillas that sickened more than 700 people in Finland.
In August 2023, 721 people fell ill with gastrointestinal symptoms in 17 schools in a Finnish municipality. Among them, 323 developed symptoms quickly during lunch or less than 30 minutes after the meal.
In three samples of tortillas produced during a limited production period, concentrations of the preservative calcium propionate above 24,000 mg/kg were measured, exceeding the maximum regulatory limit of 2,000 mg/kg, according to a study published in the journal Eurosurveillance.
Researchers measured calcium concentrations nine times higher in tortillas packaged within nine minutes of the afternoon than in products from the same batch packaged later in the day. Calcium propionate was analyzed in three high-calcium samples, and concentrations 10 times higher were found compared to samples from two later-produced tortillas.
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 baked goods to inhibit mold and extend shelf life.
Rapid onset of symptoms
Finland has a school meals program providing free lunch each 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 retrospective questionnaire-based cohort study, consumption of flour tortillas and vegetable toppings served at lunch was statistically associated with disease. Of the 721 cases, 683 were students. A vinegar odor was noted in five of nine tortilla samples.
In August 2023, authorities in the eastern Finnish town of Mikkeli received information from the central kitchen that 10 to 20 students were falling ill with vomiting and nausea 10 minutes after eating 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) have joined the investigation into the outbreak.
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 person consulted healthcare providers.
Among all cases, 167 mentioned a bad or strange tortilla taste, 24 a bad or strange smell, and 130 said the food tasted like soap or detergent.
Risk due to chemical agents
The tortillas were delivered packaged in a modified atmosphere, 18 per package, opened to school kitchens and served unheated according to the manufacturer’s instructions. The guests filled the tortillas themselves.
The tortillas served in the 16 schools consisted of two batch numbers with the same expiration date. Manufacturing and shipping to Finland involved Poland and the Netherlands. They were distributed to several locations, including community meal providers, but no gastrointestinal illnesses were reported.
Inspections of the central kitchen and the on-site and satellite kitchens did not reveal any hygiene lapses that could explain the outbreak.
In three tortilla samples, the concentrations of calcium propionate and propionic acid exceeded the maximum allowable level. Samples with elevated concentrations came from packaged tortillas between 1:24 p.m. and 1:32 p.m.
Although suspicion regarding the tortillas was later limited to a single batch and packaging time window (1:12 p.m.-4:33 p.m.), the operator destroyed both batches.
“Our results 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 foodborne outbreaks, and guidelines should exist for interrupting school meals for safety reasons,” the scientists said.
