Leslee Cohen-Lavin and her family were feeling pretty good just before the holidays. “Then all of a sudden, we each went down right when break started,” said Cohen-Lavin, of Highland Park. Her 5-year-old daughter got a fever and aches and lost her appetite. Soon, Cohen-Lavin developed a days-long fever. Finally, her husband got what felt like a head cold. They canceled most of their plans for winter break.