High levels of an additive in tortillas have been identified as the likely cause of a significant outbreak in Finland.

The Finnish Food Authority (Ruokavirasto), National Institute of Health and Welfare (THL), and local agencies investigated the outbreak, which affected more than 800 people. The incident occurred in August in Mikkeli, with mainly children falling sick.

High concentrations of the additive calcium propionate were found in tortilla samples. Ruokavirasto said this was the likely cause of school children’s symptoms. Calcium propionate is used in bakery products as a preservative. Propionic acid inhibits the growth of mold and some bacteria. 

Ruokavirasto said poisoning caused by calcium propionate was “extremely rare.”

One affected batch
Based on a survey with more than 4,000 responses carried out by officials in the Mikkeli region and analyzed by THL, tortillas were the most likely explanation for children getting sick.

A total of 812 people fell ill in the outbreak from 18 different schools. Several students said the tortillas smelt or tasted like soap or detergent.

The main symptoms of patients were stomach pain, nausea, and headache. They started quickly and were short-lived. In most patients, symptoms started less than an hour after eating, and the average duration was under 12 hours.

In studies carried out in September, sensory changes and variations in the acidity of the product were noted in some tortillas. Changes were observed only in items made at certain times of one day. Implicated products were removed from sale in August.

Calcium propionate concentrations of the suspected tortillas were 10 times higher than other tortillas. They exceeded the highest permitted use of the additive which is 2,000 milligrams per kilogram. Calcium propionate has no proven harmful long-term effects.

The Polish manufacturer and authorities in Poland are investigating the high concentrations.

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