Caterer says another firm made the meals given to the Tseung Kwan O school Fifty-eight children at a primary school in Tseung Kwan O were rushed to hospital yesterday suffering food poisoning, hours after sushi lunches were provided by a school caterer. Investigations are under way to determine the cause of the poisoning. The children complained of vomiting, stomach aches and diarrhoea one to two hours after lunch at the Hang Hau Central Shing Hang Fong Memorial Primary School. The Department of Health said initial investigations suggested it was an outbreak of 'bacterial food poisoning with a short incubation period'. Twenty students were sent to the accident and emergency department of United Christian Hospital and a further 38 to Tseung Kwan O Hospital. The 36 boys and 22 girls, aged seven to 15, were all discharged after treatment. The school's headmaster, Wong Yiu-wing, said a total of 108 pupils felt uncomfortable, but 50 did not require hospital treatment. Primary Four pupil Lam Chi-hin said: 'I ate five pieces of crab meat sushi and it tasted slightly sour. Afterwards, I had a stomach ache and diarrhoea.' Kwong Yin-fei, a Primary Three pupil, said she ate an assortment of sushi, including eggs and eel. 'After lunch, I felt nauseous and I wanted to throw up. This is the first time the school has served sushi.' The school's caterer, Best Food Company, said it provided more than 500 lunch boxes, including about 400 boxes of sushi. The rest consisted of chicken wings with rice, or spaghetti with peppered beef. But a spokesman for Best Food said the sushi was prepared for the first time by a partner firm. The boxes contained eight pieces of sushi, including pieces of cooked tuna, egg and crabstick. He claimed the sushi 'was all cooked'. A spokeswoman for the Food and Environmental Hygiene Department said although Best Food was licensed to supply meals to the primary school, its partner firm only held a food factory licence. An additional licence is required to supply schools, although the spokeswoman added: 'We cannot comment if there has been a breach in the regulations.' There are 40 licensed school caterers in Hong Kong. Licensees are required to keep cold dishes, such as sushi, at a maximum of 4 degrees Celsius at all times, including during transportation. Microbiologist Paul Chan Kay-sheung, from Chinese University, said it was important that the source of the infection be traced to help 'predict what will happen to the children'.