Officials in Finland remain stumped by a large outbreak linked to school meals.

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

Ruokavirasto reported that examining food samples has not found any typical food poisoning bacteria, toxins, or signs of microbiological spoilage.

Only sensory changes and differences in acidity have been observed in tortillas, which were suspected to be the cause of illness.

Food tests have looked for bacteria of the Bacillus cereus group and coagulase-positive staphylococci, as well as their toxins, molds, and other microbes.

Sensory issues with tortillas
Based on a survey conducted by local officials in Mikkeli, including more than 4,000 responses, which was analyzed by THL, people who had eaten tortillas were three times more likely to get sick than those who didn’t.

A total of 812 people fell ill in the outbreak from 18 different schools.

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.

Health officials said this disease picture is not typical for common causes of food poisoning, with symptoms caused by agents such as Staphylococcus aureus, Clostridium perfringens, and Bacillus cereus, usually appearing about 30 minutes to 24 hours after a meal.

Tortillas were sent to schools in large packages through a central wholesaler. Several students said they smelt or tasted like soap or detergent.

Examined tortillas have shown variations in pH levels. These changes appear to be related to part of one batch. Other foods are also being tested as part of attempts to find the source.

Information about the findings was forwarded to the authority of the unnamed European country where the tortillas were manufactured.

In 2021, a large Salmonella outbreak in Finland affected more than 700 people, with children making up the majority of patients. The implicated food was a salad with iceberg lettuce, cucumber, and peas served in several educational establishments. Officials in the city of Jyväskylä investigated the incident with the help of THL.

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