Denmark solves Cryptosporidium outbreak

A Cryptosporidium outbreak in Denmark has been traced to a type of produce from Italy.

During June and July, the Statens Serum Institut (SSI) registered 11 cases of Cryptosporidium parvum IIzeta.

The SSI, the Danish Veterinary and Food Administration (Fødevarestyrelsen), and National Food Institute investigated the outbreak and found that several patients had eaten in different canteens run by the same catering company.

Flat-leaf parsley from Italy was identified as a possible source of infection.

Six men and five women were ill. Patients were between 22 and 60 years old with a median age of 31.

Five patients lived in Sjælland, four in Hovedstaden, and two in Syddanmark. The SSI said this data should be interpreted with caution, as the agency does not receive Cryptosporidium-positive samples from all clinical microbiology departments in the country and there are regional differences in testing.

The SSI sequenced samples from patients and conducted interviews to identify the source of infection. Patient interviews showed several of them could be linked to eating in different canteens. Flat-leaf parsley from Italy was the likely source of infection.

Cryptosporidium in Denmark
Cryptosporidium parvum IIzeta was first seen in Denmark in May 2024, and five cases were registered until March 2025. This type of Cryptosporidium has so far only been reported in Denmark.

Cryptosporidiosis had been considered rare in Denmark and primarily associated with travel abroad. Cryptosporidium in humans came under national surveillance in 2023.

A study, published in the journal Emerging Microbes and Infections, assessed all cases in Denmark from 2010 to 2024. After 2021, infections increased, coinciding with the adoption of gastrointestinal syndromic testing in several local hospitals.

Most patients had no history of travel outside Denmark, but the variety of infecting species suggests a number of as yet uncovered transmission routes.

Cryptosporidium is a parasite that can cause gastrointestinal illness. The main symptoms include watery diarrhea, stomach pains or cramps, nausea or vomiting, mild fever, loss of appetite and weight loss. Symptoms usually start two to 10 days after contact with the parasite and can last for up to two weeks.

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