Also called the "stomach bug" or "stomach flu," norovirus tends to surge during the winter months.
A national surge of norovirus -- the highly contagious illness that can cause vomiting, diarrhea and low-grade fevers -- has also sickened some residents across the D.C. region in recent weeks.
Sometimes called the "stomach bug" or "stomach flu," cases of norovirus tend to balloon between November and April, according to the Centers for Disease Control and Prevention.
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In Virginia, health officials recorded an uptick in norovirus outbreaks -- defined by the CDC as two or more cases -- during the weeks of Dec. 8 and Dec. 15, data from the state show. There were 27 reported outbreaks during those weeks, twice the amount recorded over the same period last year.
During the week of Dec. 22, the number of outbreaks in the state fell to three, Virginia officials say.
Maryland does not track outbreaks by the week, according to a state health department spokesperson. As of Monday, there were 16 confirmed norovirus outbreaks this year. The state recorded 38 outbreaks in 2023 and 37 in 2022.
But outbreaks in other parts of the country could mean similar trends are happening in Maryland, said James Campbell, a pediatric infectious-disease pediatrician at the University of Maryland Children's Hospital. It's unlikely that states reporting surges to the CDC are the only places seeing more outbreaks, he said.
A spokesperson for D.C. Health said Monday that the city had no confirmed cases of norovirus.
Beyond the D.C. region, the most recent CDC data shows there were 91 outbreaks across more than a dozen states during the week of Dec. 5, up from 32 outbreaks two weeks prior. The data reflects information reported by local health departments.
Norovirus spreads easily, said Gabrina Dixon, a pediatric hospitalist at Children's National Hospital. "It can go around families, so one person gets it, the whole family can get it," Dixon said. Symptoms can appear between 12 and 48 hours after exposure and last a day or two, she said.
Children, elderly adults and immunocompromised people are at the highest risk when contracting norovirus because of how much fluid gets lost.
Overall, CDC data shows this year has seen a 36 percent increase in total norovirus outbreaks. In 2023, between Aug. 1 and Dec. 11, the 14 states included in the CDC's norovirus database reported 363 outbreaks. This year, that number jumped to 495 outbreaks over the same period.
Norovirus can spread from person to person, frequently through food. Public health officials in British Columbia issued a food recall for certain oysters this month after 77 cases of norovirus were reported in western parts of Canada. The U.S. Food and Drug Administration issued a similar warning related to the oysters.
Meanwhile in Minnesota, which reports norovirus incidents to the CDC, the health department recorded more than 40 outbreaks this month. The figure is almost twice as high as normal, according to officials.
Each year, there are about 2,500 reported outbreaks of norovirus across the country, but health experts say the true number could be higher. Norovirus is often treated at home and not reported to health officials, Dixon said.
And those who might have it are not always tested at health sites, she added. "We do see children coming in with vomiting and diarrhea," she said. "It's usually self-resolved. The biggest thing is to stay hydrated."
Dixon recommends frequent hand-washing for at least 20 seconds and cleaning household surfaces with bleach.
She also warned about increases of two other illnesses that peak in the winter: the flu and respiratory syncytial virus, more commonly known as RSV. Cases in the District are "high for the winter season," Dixon said.