This highly contagious "winter vomiting disease" is surging across the country

• It's surging as cases of whooping cough, or pertussis, are spiking and the dangers of COVID and the flu loom.
• The sickness could require medical attention or even hospitalization for immunocompromised people, the elderly and little kids, the CDC says.

By the numbers: Cases of norovirus have doubled over the last few weeks, according to new data from the Centers for Disease Control and Prevention.

• About 14% of tests for norovirus came back positive during the week of Nov. 15, double the roughly 7% positivity three months ago, the CDC data show.
• Test positivity, though imperfect, generally helps health officials understand how many people are confirmed to have an illness when it is suspected.

Flashback: December 2024 was a record-breaking month for norovirus cases, with test positivity hitting almost 25%.

• Since then, positivity rates generally began to drop nationwide, until the recent spike.

Here's what to know about the norovirus.

What is the norovirus?

Norovirus can cause extreme cases of vomiting and diarrhea due to the inflammation of the stomach and intestines, per the CDC.

• This is why some refer to norovirus as the "extreme vomiting disease."
• Norovirus is also the top cause of vomiting and diarrhea, the CDC says.
• Roughly 20 million people contract the norovirus every year, per Scientific American.
• Norovirus is different than the "stomach bug" or "stomach flu," and is not related to the flu, which comes from the influenza virus.

Norovirus symptoms to watch for:

There are common symptoms with the norovirus, which develop within 12 to 48 hours of contracting the virus, including:

• Diarrhea
• Vomiting
• Nausea
• Stomach pain
• Dehydration (often caused by extreme vomiting and diarrhea)

Yes, but: Symptoms such as fevers, headaches and body aches are less common but possible.

Who is at risk for norovirus?

Norovirus outbreaks can impact all age groups. Children and older adults are the most vulnerable to severe infections, the CDC says.

• And, per the CDC, people can get the illness many times because there are several different types of norovirus.
• Your likelihood of getting norovirus may be determined by your genes, the CDC says.

Zoom in: Anyone who consumes raw oysters or other filter-feeding shellfish could be at risk for contracting the norovirus, according to the CDC.

How does norovirus spread?

The norovirus is super contagious and spreads quickly, according to multiple health officials, mainly through drops of body fluids or contact with contaminated surfaces or food.

• "Norovirus is a human virus that is typically transmitted by the fecal-oral route," Robyn Chatman, a Cincinnati-based physician, told the American Medical Association. "That just means that we've handled something that is contaminated, and once it's on our hands, we do all kinds of things with our hands."
• The virus can linger for several days or weeks, and spread quickly through highly populated environments like nursing homes, day care centers and cruise ships, the AMA reports.

Case in point: One doctor told the AMA that someone could get the norovirus by using the same bathroom as someone who had been visiting a family member who was recovering from the bug.

Norovirus outbreaks, explained

An "outbreak" of the norovirus is defined by the CDC as when two or more similar illnesses come from a common exposure that is either "suspected or laboratory-confirmed to be caused by norovirus."

• There are about 2,500 outbreaks every year. CDC says there were 153 norovirus outbreaks reported between Aug. 1 to Nov. 13.
• Last year, the CDC said there 69 outbreaks by the final week of November. In 2023, the U.S. saw 65 outbreaks in the first week of December, AP reports.

How to prevent the spread of norovirus

Proper handwashing can help limit the spread of the illness, per the CDC.

• The CDC also recommends cooking shellfish thoroughly and washing fruits and vegetables.
• Cleaning and disinfecting surfaces can also stop the spread.

The CDC advises those infected to stay home for two days (48 hours) after symptoms stop.

Treatment for "winter vomiting disease"

There is no specific cure for the norovirus, according to the Cleveland Clinic. But symptoms typically die off within one to three days.

• Health officials recommend drinking plenty of liquids with electrolytes, rest, and eat bland foods to help manage your symptoms.

More from Axios:

Virus season roars back with "quad-demic" of illness

Your wastewater could reveal norovirus outbreaks