Everything to Know About the Rise in Norovirus Cases

Karena Peterson, 3/5/25

There has been a recent spike in norovirus—commonly called the “stomach bug”—cases as of late 2024, early 2025. While norovirus typically spikes around the winter seasons for reasons such as the clustering of people indoors, the Centers for Disease Control and Prevention (CDC) reports an unusually high number of outbreaks compared to recent years.

While last year there were only 557 outbreaks in the United States, reported by states participating in the CDC’s NoroStat data collection, between August 1, 2024, and January 15, 2025, 1,078 outbreaks were reported by the same states—nearly twice as many outbreaks.

What is Causing this Outbreak?

One possible cause of the spike is a newly prevalent strain in the United States. Norovirus, being a virus with many subtypes, has a strain named GII.17. Previously, this strain was much less common in the U.S., meaning fewer people have developed strong immunity to it. However, this strain has recently been linked to seven out of 10 cases in the United States.

Norovirus, unlike other common illnesses during winter months, such as influenza (the flu) or COVID-19, that spread through respiratory means, typically spreads through fecal-oral transmission. Dr. Roberts, a specialist at Yale Medicine, explains norovirus is highly transmissible because “A person who has been sick with norovirus sheds billions of virus particles in their stool or vomit.” In fact, as few as 10 particles are enough to cause an infection, Yale Medicine reports in its "Norovirus (Stomach Flu) Cases Are Surging: 3 Things to Know" article.

How Does Norovirus Spread?

A common setting in which this fecal-oral transmission happens is the food industry. The CDC states that norovirus is the leading cause of outbreaks from contaminated food in the United States. About 50% of all outbreaks of food-related illness are caused by norovirus, according to the CDC’s "Norovirus Facts and Stats" webpage. Norovirus is common in food service as it often spreads through the handling of ready-to-eat foods by an infected individual. Certain foods, like oysters, can also be contaminated at the source.

Norovirus is reported in the CDC’s "Norovirus Facts and Stats" webpage to typically cause 19 to 21 million illnesses per year in the United States alone. From those, there are roughly 109,000 hospitalizations and around 900 deaths, typically from people aged 65 or older. Children are also more vulnerable, with the majority of the 2.27 million outpatient clinic visits and 465,000 emergency department visits being young children.

What are the Symptoms of Norovirus?

When infected, norovirus causes gastroenteritis—inflammation of the stomach and intestines—giving it its name of “stomach bug.” Both children and adults can experience the typical symptoms of nausea, vomiting, diarrhea, headache, fevers, stomach pains, and body aches, though adults may experience more diarrhea than children. Additionally, children may also experience the complications of crying without tears, fussiness, and sleepiness.

Preventing the Spread

The CDC also states that norovirus typically costs the U.S. $2 billion per year, “mainly due to lost productivity and healthcare expenses,” according to the CDC’s "Norovirus Facts and Stats" webpage. The primary way to prevent norovirus spread is thorough hand washing. Additional measures include washing produce, sanitizing surfaces, and properly preparing seafood. As the number of cases tick up, it is important to use preventive measures to help limit the spread and impacts.

Sources

Norovirus Facts and Stats | Norovirus | CDC

Norovirus Outbreaks | Norovirus | CDC

NoroSTAT Data | Norovirus | CDC

Norovirus (Stomach Flu) Cases Are Surging: 3 Things to Know > News > Yale Medicine

Norovirus: Symptoms, Causes & Treatment