What's behind this season's norovirus surge?

According to the latest data from the Centers for Disease Control and Prevention (CDC), the number of norovirus infections continues to rise in the United States this winter, reaching levels higher than the same period last year.

Current data from CDC CrazySTAT According to the monitoring system, there were 495 incidents reported between August 1, 2024 and December 11, 2024, compared to 363 incidents during the same period last year. Additionally, the total number of norovirus outbreaks this season is higher than those reported during the 2012-2020 and 2021-2024 seasons.

Dr. Sara Mirza, an epidemiologist in the CDC's Division of Viral Diseases, said in an interview that circulating strains of norovirus change over time, which can affect disease burden and potential disease severity. He said that there is.

Mirza said the number of cases during the 2024 norovirus season (which is thought to be approximately from November to April) will reach or exceed the number of cases seen before the COVID-19 pandemic. He said there was.

The increase in cases may be partially caused by a new dominant strain of norovirus. “For the 2024-2025 fall/winter season, Genogroup 2, Genotype 17, known as GII.17, will be the most detected gene in the United States among laboratory-confirmed outbreaks reported to CDC. “Kata Co., Ltd.,'' Mirza said. “At this time, there is no indication that GII.17 causes more severe disease or affects some populations more than others, but we continue to monitor it to assess,” she said. added.

clinical key points

“Norovirus affects all age groups, but young children and the elderly are most at risk for more severe outcomes,” Mirza said. Medscape Medical News.

“Physicians treating elderly patients with acute gastroenteritis should be aware of this increased risk, especially in vulnerable patients with other illnesses or those living in congregate living settings such as nursing homes,'' said Dr. “Norovirus should definitely be included as a diagnosis,” he said.

Dr. Mirza said that when treating patients with norovirus infection during an outbreak, soap and water should be used for hand hygiene after treating patients with suspected or confirmed norovirus gastroenteritis. He added that if norovirus infection is suspected, the use of PPE is recommended for anyone in patient care areas.

Although state, local, and territorial health departments are not required to report individual cases of norovirus to CDC, health care workers must report all outbreaks of acute gastroenteritis, including suspected norovirus outbreaks, to the appropriate state, local, and local authorities. , or to the territorial health authority. said Mirza. “Health authorities are encouraged to report all suspected and confirmed norovirus outbreaks. National outbreak reporting system and carissinet” she added.

“Infection prevention measures such as thorough hand washing, cleaning and disinfecting surfaces with bleach, and patient isolation and contact precautions in public gatherings and health care settings are the best ways to prevent norovirus and prevent it from spreading to others. It’s a method,” Mirza said. Medscape Medical News.

Mirza emphasized reminding patients that alcohol-based hand sanitizers are ineffective against norovirus because the virus' protective protein shell prevents alcohol from entering and inactivating the virus. “Soap and water work to remove germs from your hands,” she said.

Cruise ship considerations

According to the CDC, cruise ships continue to be an increased risk source for norovirus. CDC's Ship hygiene program (VSP) was established to help the cruise industry prevent public health issues such as norovirus outbreaks and provide guidance on the actions to take in the event of an outbreak.

For example, the most recent norovirus outbreak on a cruise ship reported to VSP was January 4, 2025, and norovirus outbreaks on Holland America cruises from December 30, 2024 to January 8, 2025 were reported to VSP on January 4, 2025. It happened. 1.0% of the crew reported illness. Following the VSP's guidance, the ship reported enhanced cleaning and disinfection procedures, collection of stool specimens for testing and isolation of sick passengers and crew.

clinical perspective

In clinical practice, the number of norovirus cases is significantly higher than previous years, and the trend appears to be consistent across the country, said David, an associate professor of medicine and pediatrics at Rutgers New Jersey Medical School in Newark, New Jersey. – said J. Cenimo, MD. In an interview.

“Norovirus is incredibly contagious and spreads very quickly, so an entire cruise ship could be infected at once,” he said. Norovirus is notoriously difficult to disinfect and kill, he added.

Cennimo said one possible reason for the spike in cases is increased travel, especially during the holiday season, when people gather and share food. “We have seen many infectious diseases, such as pneumonia, return to levels close to pre-pandemic levels,” Cennimo said. Medscape Medical News.

To prevent norovirus, it is essential to pay close attention to hygiene and hand washing both at home and when traveling, Cennimo said. He said it was important for clinicians to report occurrences of gastrointestinal diseases so that appropriate control measures could be taken.

Visit the CDC website. norovirus prevention For more information.

Mirza and Cennimo had no financial conflicts to disclose.