ABOUT 400 doctors, nurses, social workers and other United Christian Hospital staff came down with food poisoning yesterday after a special gastronomic treat to bid farewell to their 22-year-old canteen. Hospital general manager (administration services) Grace Leung Yuen-ling said the sick employees - most of whom were too ill to work - accounted for a fifth of all staff. Staff who had lunch at the canteen on Monday were laid low by bouts of vomiting and diarrhoea within 24 hours. 'We suspected that cold dishes, including jelly fish and Japanese octopus, were the cause,' said hospital chief executive Dr Tse Chun-yan. 'They came from our two food suppliers and the names of the suppliers were provided to the Department of Health for investigation,' he said. The Medical Social Services Department was forced to close because all of its social workers were sick. Queues of people seeking treatment formed at the out-patients department and the pharmacy. Many complained they had to wait for hours to see doctors, be medically examined or collect medicine. About 400 staff were treated and released, but two men and 13 women - including six nurses - remained in hospital last night. The illness broke out after a 'thank you' lunch was arranged for 1,300 staff on the canteen's last day of operation. An Urban Services Department spokesman said the canteen was unlicensed, but was checked by inspectors once a month. Its record was 'satisfactory'. Department spokesman Dr Mak Kwok-hang said tests should pinpoint the source of the bacteria by the end of the week. The hospital's new canteen opened yesterday. Dr Tse said administrators had called on staff to cancel their holidays and return to work. He insisted emergency services had been maintained, but acknowledged some patients had lengthy waits for treatment.