Public health officials in Sweden are investigating an outbreak of Cryptosporidium infections.

The Public Health Agency of Sweden (Folkhälsomyndigheten) said it was trying to find the source of the outbreak caused by the parasite Cryptosporidium, which causes cryptosporidiosis.

Since mid-December 2023, 68 people from 14 regions have been infected. The majority of patients are from Halland and Jönköping.

Of cases, 72 percent are women, the average age is 41 and 79 percent are in the age group 21 to 60 years old. Data shows the latest case of illness onset was early January.

Typing of some samples showed that 13 of 18 belonged to the same type of Cryptosporidium, which indicates that patients have a common source of infection, said health officials.

Hoping interviews give a clue

Livsmedelsverket (the Swedish Food Agency) and affected local infection control units are also attempting to find the source, which is suspected to be some type of fresh food.

Information about what outbreak cases ate before becoming ill is gathered via interviews and the collection of questionnaires. Answers will be compared to what people in a healthy comparison group have eaten to assess whether there are foods that outbreak cases have consumed to a greater extent than the comparison group.

In October 2023, goat milk cheese was suspected to be the source of an outbreak of cryptosporidiosis in Sweden that sickened seven people. The incidents are not thought to be linked.

In 2022, 716 cryptosporidiosis cases were reported in the country. A peak in infections is usually seen in late summer and autumn. The majority of reported cases were infected in Sweden and 146 people were infected abroad.

Six cryptosporidium epidemics sickened 208 people. Epidemiological investigations in one outbreak pointed towards contaminated lettuce in ready-to-eat green leaf-mixes as the probable cause of infection.

The incubation period varies from two to 12 days. Symptoms, which normally last for up to two weeks, include moderate to severe watery diarrhea, low-grade fever, cramping abdominal pain, nausea and vomiting.