CHICAGO (Reuters) - For the past two weeks, high school nurse Colleen Kahler has been on high alert. Her office, which typically treats routine ailments such as sore throats, stomach aches and pulled muscles, has been transformed into a screening center for an unlikely disease with a name that recalls a bygone era -- whooping cough. "We became a triage unit," says Kahler, health services coordinator at New Trier High School in Winnetka, Illinois, a tony suburb of Chicago. "The phones were literally ringing off the hook," she said. "We were fielding questions from parents, physicians and students." Health experts...