Aims: In March and April 2009, the Norwegian Institute of Public Health was notified about two groups of schoolchildren with gastroenteritis following a stay at a Norwegian wildlife reserve. Although at first considered a typical norovirus outbreak, an investigation that considered other possibilities was initiated.
Methods: A retrospective cohort study was conducted among schoolchildren visiting the reserve in the relevant weeks. A web-based questionnaire was distributed by email. Faecal samples of visitors and employees were analysed. The premises were inspected, and water samples and animal faeces analysed.
Results: We received 141 replies (response rate 84%); 74 cases were identified. Cryptosporidium oocysts were detected in faecal samples from 9/12 (75%) visitors and 2/15 (13%) employees. One employee diagnosed with Cryptosporidium infection helped in the kitchen. Additionally, one pupil was diagnosed with norovirus infection. No food item was identified as a source of the outbreak. Pathogens were not detected in water samples taken in week 12, one week from the start of the outbreak. Escherichia coli, but not Cryptosporidium oocysts, were detected in water samples taken one month later.
Conclusions: Although Cryptosporidium is seldom considered as an aetiological agent of gastrointestinal illness in Norway, this outbreak indicates that it should not be excluded. In this cryptosporidiosis outbreak, the largest in Norway to date, the transmission vehicle was not definitively identified, but a food handler, water, and animal contact could not be excluded. We recommend improving hand hygiene routines, boiling drinking water, and emphasise that people who are unwell, particularly those working in catering, should stay away from work.