Cases were defined as persons with sudden gastrointestinal illness (at least one symptom: vomiting, diarrhoea, abdominal cramps or nausea) who had eaten buffet lunch at the VIP restaurant on 12 or 13 June. Controls were defined as persons who had eaten buffet lunch at the VIP restaurant on 12 or 13 June, without any gastrointestinal symptoms. Non-hospitalised cases and controls were contacted using information provided by the event organiser.