A top fashion designer quarantines a sneezing underling, forcing her to work in a closet. An industry P.R. executive makes colleagues douse their hands with Purell. Germ-phobic magazine editors are powerblasting offices with antiseptic wipes and Lysol. Such is the dread gripping the fashion world as it prepares for New York Fashion Week, beginning Feb. 7, with a killer flu and a stomach-bug norovirus on the loose. The eight-day event, when fashionistas from around the world pack into small spaces to attend runway shows and parties — only to cram onto the same flights and repeat the process in London, Milan and Paris — is always an occasion for sickness paranoia. In past years, sniffles in the front row could prompt icy stares and social ostracism. But with this season's flu panic, the fear is approaching hysteria. Stressed-out designers recoil in horror if someone coughs within earshot. Frail models shiver their way between fittings, terrified someone will spy their runny noses