Some health experts worry that the variant GII.17 responsible for last year's spike may have mutated and become more contagious.A nasty, highly contagious form of norovirus called “winter vomiting disease” is spreading across the country, according to an analysis of wastewater at NUMBER surveillance sites in the state. Norovirus cases typically spike after Christmas and New Year’s gatherings, but the number of new cases in November showed a notable increase, according to Centers for Disease Control and Prevention data. The CDC tracks norovirus through voluntary reporting from clinics and state health departments, but says such data is unreliable because most...