On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 

{'answer_start': [1775], 'text': ['40']}