Norovirus cases are surging in the United States, with 455 outbreaks reported since the beginning of September. More than 90 of those occurred in the first week of December – one of the highest reported rates since records began in 2012.

The actual number of outbreaks is likely far higher because only 14 states contribute to the Centers for Disease Control and Prevention’s “NoroSTAT” reporting system.

Rising disease rates are also reflected in an increasing number of positive tests for norovirus, which the CDC is using to monitor the spread of the disease across the country. These saw a sharp increase from 10.6% in the week ending November 16th to 22.02% in the week ending December 21st. High numbers of cases have also been reported in other countries, including the United Kingdom

Typically, about 2,500 outbreaks are reported in the U.S. each year, with most cases occurring between November and March and peaking in February. Experts say the disease could spread early this year as people socialize more readily than they have in years.

What is Norovirus?

Norovirus, also known as “stomach flu,” “stomach virus,” and “winter vomit,” is a highly contagious seasonal illness that causes gastrointestinal distress. In fact, it is responsible for more vomiting, diarrhea, and foodborne illnesses than any other illness in the country.

Noroviruses spread when small particles of infected feces enter the body through the mouth. Transmission often occurs through direct contact with an infected person, touching a contaminated surface (and then the mouth), or consuming contaminated food or drinks.

Once inside the body, norovirus enters the intestines, where it attaches to the sugars called “oligosaccharides” that line the small intestine. Once there, it can cause inflammation of the intestines or stomach, which can lead to severe gastrointestinal illness.

What are the symptoms of norovirus?

Noroviruses often cause nausea, stomach pain, vomiting and diarrhea. It can also cause certain flu-like symptoms such as headache, fever and body aches. Although it is often called the “stomach flu,” it is not caused by the influenza virus.

Vomiting and diarrhea can quickly lead to dehydration. Therefore, people with this disease should try to drink water, even if it is difficult to keep fluid intake low. Drinking very small, frequent sips of water may make it easier to stay hydrated.

Symptoms appear relatively quickly after exposure to norovirus — usually within about 12 to 48 hours, according to the CDC. They usually end one to three days later. But a person can continue to spread the disease through their feces for several days after they feel better.

How can I protect myself from norovirus?

The best way to prevent norovirus is to wash your hands frequently and thoroughly – especially after using the toilet, changing a baby or caring for a sick person, and before eating. Avoid touching your face as this can bring the virus closer to your mouth.

Keep frequently touched surfaces such as doorknobs and countertops clean, and wash potentially contaminated clothing and sheets at high temperatures to kill any remaining viruses.

It’s also important to wash fruits and vegetables before eating them and to make sure shellfish are cooked thoroughly. The CDC recommends completely avoiding raw shellfish like oysters because it can cause illness and even death.