The CDC says cases of the norovirus are surging in part of the U.S., with the most cases in New York, Florida and California.

Norovirus is a highly contagious stomach bug. In New York City, the latest numbers show more than 1,000 cases in December. During the same time last year, there were fewer than 500 cases.

The city’s Department of Health is urging New Yorkers to follow prevention tips including handwashing and surface disinfecting.

Dr. Susannah Hills, a surgeon and assistant professor at Columbia University, joined “News All Day” on Tuesday to talk more about the virus.