Cases of the dreaded "vomiting virus" are spiking around New York City, marking the start of the stomach-flu season, the Health Department reported Thursday.

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Emergency rooms are now seeing a total of about 500 cases of norovirus a day compared to a typical daily average of 300. The virus, also a plague aboard cruise ships over the past few years, can cause days of severe vomiting and diarrhea along with cramps, the chills and fevers.

"The best way to stop the spread of norovirus is to wash your hands regularly with soap and stay home from work or school if you're sick," said Dr. Sharon Balter, of the Health Department's Bureau of Communicable Disease.

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Virus Shuts Down Schools in Connecticut

The norivirus is also suspected of sickening scores of students in Connecticut. The outbreak promoted officials in East Lyme to close all five public schools.

The idea is to prevent the further spread of a virus blamed for keeping many middle-school students home sick Wednesday and Thursday.

School officials say at East Lyme Middle School more than 20 percent of the 921 students stayed home Wednesday or were sent home early from the nurse's office.

Officials say the problem is likely a norovirus, the kind of virus known for causing outbreaks of stomach flu on cruise ships.

Attendance this week at all other East Lyme schools has been normal.

Associated Press contributed to this story