(NEWSnet/AP) — Cases of norovirus are climbing in the Northeastern U.S., Centers for Disease Control and Prevention said Thursday.

About 12% of most recent norovirus tests sent to CDC were positive, but the proportion was about 16% in the Northeast U.S. 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 and diarrhea, norovirus outbreaks are common on cruise ships, nursing homes, schools and other places where people are in close contact.

Some things to know

Norovirus infection is caused by a group of viruses that spread easily. It can take as few as 10 viral particle  to make someone sick, said Dr. William Schaffner, a infectious disease expert at Vanderbilt University Medical Center.

A person can go from slightly unwell to miserable within hours. It typically lasts two or three days. Most people recover fully.

Norovirus can spread from person to person, in food or water or on contaminated surfaces. Because it’s so contagious, a handshake or the touch of a contaminated door knob or handrail can be enough to cause illness.

There is no medication to treat norovirus. Dehydration from vomiting and diarrhea is the primary worry, so those most at risk include young children, older people and those with a weakened immune system.

It’s important to replace fluids by sipping water, soda or other beverages — except coffee, tea and alcohol — during illness, Schaffner said. Anyone experiencing symptoms of dehydration should seek medical help, he added

The best defense against norovirus infection, especially during peak winter season, is frequent hand-washing.

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