The president of Japan's largest dairy goods producer , Tetsuro Ishikawa, has resigned following the country's worst outbreak of food poisoning for thirty years.More than eleven thousand people have been affected by contaminated milk from a dairy in the city of Osaka in western Japan; about a hundred and sixty people needed hospital treatment.Local authorities ordered the company, Snow Brand Milk Products, to shut its plant at the weekend after people began to fall ill after drinking the company's low-fat milk. The milk was found to contain bacteria which caused diarrhoea and nausea.The cause of the outbreak was traced to bacteria in a valve in the milk production-line which had not been properly cleaned.