So, there’s this thing going around NYC. Your guide to navigating the norovirus.

A viral stomach bug has some New Yorkers camping out in their bathrooms this winter.

New York City, like the rest of the country, is in the midst of a surge of norovirus cases, according to the city health department. The easily spread virus typically causes intense vomiting and diarrhea that last for one to three days, although people can remain contagious for another two weeks after that, according to the U.S. Centers for Disease Control and Prevention.

There were 1,264 cases of norovirus reported in the city in December, compared with fewer than 500 cases reported that month in each of the previous two years, the health department said. But department spokesperson Chantal Gomez cautioned that most cases do not get reported, so these figures are likely an undercount.

Norovirus is not new. The United States typically has about 2,500 norovirus outbreaks a year, with more occurring between November and April, according to the CDC. But the number of outbreaks this season has been unusually high. During the week of Dec. 5, 91 outbreaks were reported across the country — more than have been reported that week since at least 2012, according to the latest CDC data.

Many of this year’s outbreaks are associated with a new strain of the virus known as GII.17, which experts say may be evading immunity. A different, more familiar strain has dominated for the past decade or so.

While some associate the stomach bug with cruise ships, those vacation-ruining cases only account for about 1% of all outbreaks that get reported, the CDC says. Other common settings for norovirus outbreaks include restaurants, health care facilities, schools and child care centers.

Beyond staying hydrated, there’s no specific treatment for norovirus, said Dr. Mahesh Polavarapu,  medical director of the emergency department at NewYork-Presbyterian Westchester. But most people who get infected are able to weather the symptoms at home, he said.

Still, norovirus causes more than 100,000 hospitalizations and 900 deaths in the U.S. on average each year, according to the CDC.

Polavarapu estimated his ER is seeing twice as many patients coming in with norovirus than in a typical winter.

Those who come in, he said, range from “young children all the way up to the elderly patient population with multiple medical issues.”

Here are some expert tips on how to avoid norovirus this winter — and what to do if you get it.

How does norovirus spread?

There are a variety of different ways to catch norovirus, according to the CDC. It can spread through direct contact with someone who’s infected, or it can be contracted by eating contaminated food, like other forms of food poisoning.

You can also get norovirus by touching objects or surfaces that are contaminated and then putting your hands in your mouth without washing them first.

How can you avoid catching — or spreading — the stomach bug?

Hand-washing with soap and water is key, as hand sanitizer will not do the trick in the case of norovirus, experts say.

Those who work in settings where norovirus commonly spreads, such a restaurants, should be extra diligent, said Dr. Jessica Justman, an epidemiologist at Columbia University’s Mailman School of Public Health.

“ I'm not about to say, ‘Don't eat in a restaurant,’” she said. “I don't think that's realistic. I think that we can all be thoughtful about washing our hands before we eat and after we eat.”

Justman and other experts emphasized that those who are not feeling well should stay home from school or work to avoid spreading norovirus or any other illness. And the CDC notes that those who are sick should not be handling or preparing others’ food.

“ I want to hope that people who are working in food service settings are not coming in when they feel ill,” Justman said. “But it’s tricky, right? Because people won't get paid if they don't come into work.”

While restaurant workers may have to forgo tips if they stay home, under New York law all part- and full-time workers, including those in the service industry, are entitled to take sick days. That sick leave must be paid, unless the business has fewer than five employees and brings in less than $1 million per year.

Since norovirus can also spread on surfaces, she said, anyone who has the illness or is caring for someone who is sick should be careful to sanitize door knobs, countertops and any other surfaces the sick person might have touched. The CDC recommends using a bleach solution to disinfect surfaces, as well as soap and hot water, and says a sick person’s clothes should be laundered at the highest available temperature.

Oysters have also been linked to some recent outbreaks. The CDC recommends cooking oysters and other shellfish, rather than eating them raw.

What are the symptoms of norovirus?

In addition to nausea, diarrhea, vomiting and stomach pain, norovirus may also come with headaches, body aches and a fever.

Symptoms of dehydration to watch out for include decreased urination, dry mouth and throat, and feeling dizzy when standing up, according to the CDC.

What should you do if you get it?

Doctors say hydration is key, especially with drinks that can replace the body’s lost electrolytes, such as Gatorade or Pedialyte.

“That’s especially true for young kids and elderly people because in those people, fluid shifts and dehydration can be a lot more dangerous than for a 30-year-old with no medical problems,” said Dr. Rabia De Latour, a gastroenterologist at NYU Langone Health.

Those who are sick should stay home and self-isolate, De Latour added.

When should you get professional medical help?

While most people will start to feel better on their own after a couple of days, Polavarapu said there are some key indications that a patient needs to go to the ER. That includes high fevers, severe abdominal pain that lasts for more than two to three days, or “if you ever feel like you’re going to pass out.”

He added that symptoms such as blood in the stool that are not typical of norovirus are “a red flag that you should be evaluated.”

Is there a vaccine?

Multiple norovirus vaccines are currently in development, including one from Moderna that is in its third phase of clinical trials. The company announced it was recruiting for the trial in September.

This article was updated with information about workers' "sick day" protections under New York state law.