Stomach flu cases are on the rise in the Washington metropolitan area and across the United States as cold weather and the holiday season push more people indoors.
Nationwide, the Centers for Disease Control and Prevention reported 91 outbreaks of norovirus, the formal name for the stomach bug, during the week of Dec. 5, 2024. That is up from 69 outbreaks over the Thanksgiving holiday and 32 outbreaks the week of Nov. 21, 2024.
Although the District of Columbia Health Department has not reported any confirmed cases, both Maryland and Virginia have been hit hard by this national spike in norovirus outbreaks.
Virginia health officials recorded 27 norovirus outbreaks, defined as two or more cases, during the week of Dec. 8 to Dec. 15, 2024, twice the amount recorded over the same period the year before.
Maryland does not count outbreaks week by week but recorded 16 confirmed outbreaks in the 2024 season, compared to 38 in 2023. Outbreaks in other neighboring states, however, could signal there are similar trends in Maryland.
Here is everything to know about norovirus.
Why is norovirus surging now?
Norovirus outbreaks peak in the U.S. during colder winter months, particularly around the holidays and when people are crowded indoors.
Rates of norovirus infections were “unusually low” during the 2020-2021 season due to shutdowns during the COVID-19 pandemic, according to the CDC, but the number of norovirus infections returned to a closer-to-normal baseline for the 2021-2022 season and forward.
Much like influenza infections, people can be infected with norovirus multiple times throughout their lives because there are multiple different types of specific noroviruses that cause similar symptoms.
In years when a new strain of the virus circulates, the CDC estimates that there can be up to 50% more norovirus illnesses.
It is possible to develop immunity after a norovirus infection, but scientists do not know exactly how long protection lasts.
What are the symptoms?
Symptoms of norovirus typically develop within 12 to 48 hours after exposure, the most common symptoms being diarrhea, vomiting, nausea, and stomach pain. Fever, headaches, and body aches can also emerge.
Severe cases of the illness with multiple bouts of diarrhea and vomiting a day can lead to dehydration, especially in young children, older adults, and people with underlying conditions.
Decreased urination, dry mouth, unusual sleepiness, and dizziness upon standing are common symptoms of dehydration.
Most people recover within one to three days.
Who is most at risk?
The CDC estimates that there are nearly 1 million pediatric medical visits annually in the U.S. for norovirus cases. Children under 5 and seniors over 85 are most at risk.
By age 5, one in 110,000 children will have died from norovirus, and one in 160 will be hospitalized.
Worldwide, there are about 200 million cases of norovirus in children under 5 each year, resulting in 50,000 child deaths, mostly in developing countries.
How contagious is norovirus?
Norovirus is contagious from the onset of symptoms until several days after symptoms resolve. Even people who have recovered from symptoms can still spread the illness to others for up to two weeks after symptoms have resolved, according to the CDC.
Norovirus spreads through particles of feces or vomit from an infected person to an uninfected person.
Exposure through contaminated food and water poses high risks, such as if a person with norovirus touches food with their bare hands or virus particles land on food on an open surface.
What are the treatments? Is there a vaccine?
There is no vaccine for norovirus to prevent infection, but Moderna is working on an mRNA vaccine to prevent moderate to severe symptoms from the infection.
As of late September 2024, Moderna’s norovirus vaccine had reached its Phase 3 clinical trial, the last stage in testing before a drug receives approval from the Food and Drug Administration.
In the meantime, basic disease prevention precautions, such as thoroughly washing your hands, staying home when you are sick, and disinfecting contaminated surfaces, are the best ways to prevent spread.
Symptoms of norovirus typically resolve on their own, so supportive care measures are usually all that is needed to recuperate.
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Rehydration is vital when sick with any illness that causes vomiting and diarrhea. Drinking plenty of water, sports drinks, or other oral rehydration solutions is essential for preventing dehydration.
High-risk individuals or patients with severe symptoms may require IV fluids in a hospital setting.