Denmark has reported a dozen cases of a new variant of Cryptosporidium parvum, with work ongoing to find the source.
The Statens Serum Institut (SSI) has registered 12 cases of Cryptosporidium parvum IIzeta since May.
SSI, the Danish Veterinary and Food Administration (Fødevarestyrelsen) and the National Food Institute are investigating the outbreak.
Seven men and five women are sick. Patients are aged between 20 and 60 years old with a median age of 31. They live in different regions of the country with five cases each in Hovedstaden and Sjælland and two in Syddanmark.
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 activity.
New type of Cryptosporidium
SSI is responsible for sequencing samples from sick people and conducting patient interviews to try and identify a possible source of infection.
The novel variant of Cryptosporidium parvum was first seen in Denmark in May 2024, and eight cases had been registered up to March 2025. Based on current information, this type of Cryptosporidium parvum has only been found so far in Denmark.
Outbreaks of Cryptosporidium have previously been recorded in Denmark and other Nordic countries, where the suspected source of infection was vegetables or salads.
One international outbreak in 2023 included six Danish cases but the source was not known.
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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