A new flu variant spreading overseas may set the stage for another tough winter in the United States, experts warn. The strain, called subclade K, has caused a rise in flu cases in the United Kingdom, Canada and Japan. And now signs suggest it is beginning to take hold across the United States as flu activity rises. According to the latest U.S. Centers for Disease Control and Prevention FluView report , reported flu activity in the United States remains low but is climbing quickly. Last year's