As many as 3,000 school children in 40 schools throughout Copenhagen were served listeria-infected food, city officials have warned.

In a letter to parents, the City of Copenhagen said that listeria was found in tzatziki served to school kids as part of a public-run lunch program. 

 “We are writing to you because your child has eaten EAT [the name of the school food programme, ed.] on Tuesday, November 11th and it has now been found that there was listeria in the tzatziki,” the letter reads, according to broadcaster DR. 

 The EAT programme delivers lunch to 40 different schools and the infected tzatziki was one of two lunch options offered on November 11th. According to a city official, around 3,000 of the up to 5,000 children who get their meals from the programme are through to have chosen the infected dish. 

 “We are clearly taking this very seriously, and are currently following all of the recommendations from Fødevarestyrelsen [the Danish Food and Veterinary Administration, ed.] in order to ensure it doesn’t happen again,” Lina Maria Johnsson, the head of the city’s health department, told DR. 

 It is uncertain if the listeria stems from the cucumber, garlic or yoghurt used in the tzatziki, or from unhygienic conditions at EAT’s kitchens.

Denmark has seen numerous listeria outbreaks this year. The most serious of which, an outbreak that was traced to the deli meat rullepølse, has killed 17. In another incident, listeria in a soup served at two public hospitals killed three.