The Centre for Health Protection was investigating another case of a child with a kidney stone suspected of being caused by melamine contamination in milk products. The case involved an eight-year-old boy from Yuen Long and was reported by a private hospital. He was later admitted to Princess Margaret Hospital and was in stable condition. He had drunk three packs of tainted Yili Pure Milk a week since 2003, the centre said. It was the eighth such case reported to the centre.