Norovirus rates are increasing. Here’s what you need to know.

It’s that time of year.

Rates of norovirus, a nasty disease that causes gastrointestinal upset, are increasing across the United States, according to data from the Centers for Disease Control and Prevention.

“This is the season where it increases,” said Catherine Troisi, an infectious disease epidemiologist at UTHealth Houston. “It happens all the time, but cases typically increase…from late fall through winter, probably because people are indoors.” This allows the virus to spread more easily.

“TTypically we see it in two scenarios. The first is outbreaks due to common exposure, like when you hear about lots of people on a cruise ship experiencing nausea and vomiting,” Dr. Donald Dumford, an infectious disease physician at the Cleveland Clinic, told HuffPost via email. “The second is sporadic cases, which seem to be more common during the winter months.”

The virus also tends to be common in nursing homes and also often occurs when people eat raw oysters.

“It’s not necessarily surprising to start seeing an increase at this time of year. Outside of these common source outbreaks, like cruise ships, norovirus is also known as winter vomiting sickness,” Dumford added. “We see a usual increase in cases throughout the winter months.”

The disease appears to spread more easily in cooler weather, he added: “and is able to survive longer on surfaces during this time.

Norovirus tends to cause nausea and vomiting, but can also cause fever and diarrhea, Dumford said.

Most people stay sick for one to three days and recover well at home, according to Troisi. (Be sure to stay hydrated if you get sick.) It may last longer, however, and lead to complications requiring medical attention.

“If you start to have a fever or blood in your stool, call your doctor, as this may be a sign of a more invasive type of gastrointestinal infection that may require antibiotics,” Dumford said.

If you notice you’re feeling dizzy because of dehydration from diarrhea or vomiting, you should see a doctor or go to the emergency room — “you may need IV fluids,” Dumford said.

“It’s a very contagious virus,” Troisi said. “It can persist on surfaces for up to two weeks and therefore spreads very easily.”

The best way to reduce the risk of getting sick is simply to wash your hands – and wash them well. “There have been studies on proper hand washing…a majority of people, including those who handle food, do not wash their hands properly,” Troisi said.

That doesn’t mean they don’t wash their hands at all, but they probably don’t take off their rings and wash their hands for a full 20 seconds, she said. You must wash your hands for the duration of “Twinkle Twinkle Little Star.”

It’s also not enough to pour a little sanitizer on your hands before sitting down to a meal. “Alcohol-based hand sanitizers are not effective at killing norovirus,” Dumford said.

“Hand sanitizer is great for other pathogens like flu, COVID and other respiratory viruses, but when trying to prevent the acquisition of certain gastrointestinal viruses, including norovirus, soap and water is the norm,” Dumford said.

According to Troisi, you should wash your hands before eating, after using the bathroom, after changing diapers, and when caring for sick people. “If you know there are norovirus outbreaks in your community, then even (after) shaking hands, you would want to wash your hands,” she noted.

Washing your hands and other good hygiene habits will reduce your chances of getting this vomiting illness, but will not eliminate your risk of getting sick.

If you get sick, stay away from others. “If you have vomiting (or) diarrhea, stay home while you are still sick,” Dumford said. “Also be sure to wash your hands frequently with soap and water to avoid getting norovirus on your hands and then contaminating shared surfaces.”

It’s also a good idea to refrain from cooking for other people for two to three days after your symptoms disappear, Dumford added. This will help keep those around you healthy.

Again, watch for any warning symptoms such as dehydration, fever, and blood in your stool. If you notice any worrying symptoms, seek medical attention.

According to Troisi, there is a relatively new strain of norovirus that has been infecting humans since the beginning of this year.

It’s impossible to know what that means for norovirus rates this winter, but “it may be that this year is a little worse than other years with this new strain,” she said.

Children tend to contract norovirus more than adults, but the illness can infect anyone, making good hand hygiene and staying home when sick are crucial as we head into another season of illness.