HEALTH Department officials have linked three Shenzhen farms to the latest outbreak of vegetable contamination, and urged Chinese authorities to take action to stop further scares. A couple and a 61-year-old woman were admitted to hospital on Wednesday after eating suspected contaminated choi sum, bringing to 24 the number of people since Monday to suffer nausea and diarrhoea. A Department of Health spokesman yesterday said the tainted vegetables possibly came from three farms in Shenzhen, but did not identify them. ''We informed Shenzhen Commodity Inspection Bureau to investigate and take follow-up action,'' she said. They were now screening about 70 samples at the border of Man Kam To, compared with the regular screening of about 40 samples a day. Health inspectors destroyed three tonnes of suspect vegetables intercepted on a lorry at the Man Kam To border. The senior manager of the Vegetable Marketing Organisation, Edward Lai Kwok-yan, said the price of choi sum and pak choi yesterday plummeted by about 30 per cent on fears of poisoning. Mr Lai said they would increase the number of samples checked in the market to 200 if the situation worsened.