A 40-year-old man presented to hospital complaining of vomiting. He described a 2-day history of abdominal pain associated with vomiting and diarrhoea. He denied experiencing fevers, cough or urinary tract symptoms. He had no unwell contacts and had not travelled abroad in the past year. His past medical history included bipolar affective disorder, for which he took a total of 1200 mg lithium daily in divided doses. This dose had recently been increased by the community mental health team due to recurrent episodes of mania.