Norovirus Cases Surge Across California, New Strain Fuels Concerns
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A highly contagious virus, commonly known as the “vomiting bug,” is experiencing a resurgence in California, prompting warnings from health officials about a new subvariant that could significantly increase illness this season. Rising concentrations of norovirus detected in wastewater across the state, notably in Los Angeles County and the San Francisco Bay Area, indicate increased circulation of the disease, according to the california Department of Public Health.
National increase in Norovirus Infections
The increase in norovirus cases isn’t limited to California. Nationally, the rate of positive norovirus tests has climbed from 8.66% two months ago to 11.69% as of the week ending November 22. The Western U.S. is experiencing an even more pronounced rise, with a positivity rate of 14.08%, up from 9.59% during the same period, data from the U.S. Centers for Disease Control and Prevention (CDC) reveals.
Norovirus is the leading cause of vomiting and diarrhea in the United States, and outbreaks typically occur during the cooler months, between November and April.
A New Strain Emerges: GII.17
Complicating the situation is the emergence of a new norovirus strain, designated GII.17. The CDC warns that this strain could lead to 50% more illness compared to typical seasons. “If your immune system isn’t used to something that comes around, a lot of people get infected,” explained Dr. Peter Chin-Hong, an infectious diseases expert at UC San Francisco.
During the 2024-25 winter season, GII.17 supplanted the previously dominant strain, GII.4, which had been responsible for over half of national outbreaks for the preceding decade. scientists at the CDC believe the ancestor of GII.17 originated from a subvariant that caused an outbreak in Romania in 2021. Last winter saw GII.17 responsible for approximately 75% of all norovirus outbreaks nationally, coinciding with a particularly severe season that began unusually early.
Symptoms and When to Seek Medical Attention
Severe cases involving prolonged vomiting, diarrhea, and dehydration may require intravenous hydration. Children under the age of 5 and adults 85 and older are at the highest risk of requiring emergency medical care.
Prevention and Transmission
The primary mode of norovirus transmission is through the accidental ingestion of water or food contaminated with fecal matter, or by touching contaminated surfaces and then touching the mouth. Symptoms typically develop 12 to 48 hours after exposure.
Crucially, hand sanitizer is ineffective against norovirus, making thorough handwashing with soap and water for at least 20 seconds essential. the CDC recommends humming the “Happy Birthday” song twice to ensure adequate scrubbing time, or, as Dr. Chin-Hong suggests,the chorus of Kelly Clarkson’s “As U Been Gone.”
If someone in your household is infected, diligent cleaning of surfaces is vital, as the virus can spread easily through respiratory droplets. Food possibly contaminated with norovirus should be discarded, as the virus is relatively resistant to heat, surviving temperatures up to 145 degrees. Even a small number of viral particles – as few as 10 – can cause infection, significantly less than the thousands required for a salmonella infection.
Individuals are most contagious when symptomatic, but can remain infectious for up to two weeks after recovering. The CDC advises staying home for 48 hours after symptoms subside and recommends washing laundry in hot water. Norovirus can spread rapidly in enclosed environments such as schools, cruise ships, day-care centers, and prisons. A recent outbreak was reported on the AIDAdiva cruise ship, which set sail from Germany on November 10, affecting 4.8% of the 2,007 passengers onboard.
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While everyone is susceptible to norovirus, babies are particularly vulnerable due to the risk of necrotizing enterocolitis, a life-threatening intestinal inflammation. Individuals with compromised immune systems may experience prolonged diarrhea as their bodies struggle to clear the virus.
