No 51/52a - 2020

Microsporidia disease outbreak

In collaboration with the Danish Veterinary and Food Administration, Statens Serum Institut (SSI) is currently investigating a disease outbreak in a company caused by a micro-organism that had not previously been recorded as the course of disease outbreaks in Denmark. The microorganism is a species of microsporidia coined Enterocytozoon bieneusi, which is assumed to have been transmitted from foods.

In the month of October, a company in the greater Copenhagen area reported more than 70 cases with diarrhoea among its employees. Stool samples tested negative to the viruses and bacteria usually associated with diarrhoea in Denmark, and the samples were therefore submitted to the SSI for further testing to identify any parasites. To date, the samples of 11 persons have tested positive for Enterocytozoon bieneusi, a microsporidia species. This is not a microorganism frequently seen in Denmark, and we have not previously detected any disease outbreaks caused by it. In 2009, Sweden witnessed an E. bieneusi outbreak in a hotel. Then, sliced cucumber was identified as the source of infection.

Route of infection and course of the disease

E. bieneusi is spore-producing and the spores are typically transmitted when excreted in the urine and faeces from infected persons. The spores can survive for a considerable amount of time in the environment. Typically, transmission is faecal-oral (i.e. transmission directly or indirectly from faeces, including via food and drink). The infection may cause intense and prolonged diarrhoea, abdominal pain and nausea. Furthermore, influenza-like symptoms such as fever, headache, muscle aches and fatigue may present. The infection is usually self-limiting and requires no treatment.

The disease may run a more severe course in immunocompromised persons, i.e. patients with known immunodeficiency (congenital or acquired, but not including patients with diabetes), or patients who, for a range of different reasons, receive immunomodulating medical treatment. Management of microsporidiosis is a specialist task. Thus, relevant patients should be referred by their general practitioner to a department of infectious medicine.

Diagnostics and typing

The SSI tests for E. bieneusi using PCR as well as microscopy. The current cases were detected by PCR. The laboratory results from the ongoing investigation indicate that spores may be excreted in the stools of infected persons for a minimum of 15 days.

Around 500 genotypes of E. bieneusi have been described. Preliminary typing data indicate that genotype C may be the cause of the current outbreak. In this way, the outbreak is similar to the Swedish outbreak observed ten years ago. That outbreak involved more than 100 persons and also involved genotype C.

Normally, E. bieneusi is only rarely observed in the stool samples received for testing at the SSI, and therefore the prevalence in the general population is presumably extremely low. Even so, genotype C has been detected in some sewage samples in Sweden. Despite the fact that E. bieneusi is present in a wide range of animals, genotype C is believed not to be zoonotic.

Epidemiological work-up

The investigation of the disease outbreak is ongoing. The source of the outbreak has yet to be established. Currently, E. bieneusi infection has only been recorded in persons associated with the company, but we encourage Danish doctors to be attentive to patients with prolonged diarrhoea with no obvious cause, particularly in immunocompromised persons and cases with prolonged symptoms.

(R. Stensvold, H. V. Nielsen, Department of Bacteria, Parasites and Fungi, L. Muller, L. S. Vestergaard, Department of Infectious Disease Epidemiology and Prevention)