Norovirus illnesses are up in some places. Here's what you need to know

Cases of norovirus, a nasty stomach bug that spreads easily, are climbing in the Northeastern U.S., the Centers for Disease Control and Prevention reported Thursday.

Nationwide, about 12% of most recent norovirus tests sent to the CDC were positive, but the proportion was about 16% in the Northeast, the agency said. That compares with nearly 10% of norovirus tests in the Midwest and South and nearly 13% in the West.

Characterized by the sudden onset of vomiting, diarrhea and general feelings of misery, norovirus outbreaks are notorious on cruise ships, nursing homes, jails, schools and other places where people are in close contact.

Here's what you need to know about this wily germ: