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As summer approaches, a highly contagious vomiting virus known as norovirus is making an unusual surge across the United States, despite typically being associated with the colder winter months.
In Southern California, hikers trekking the Pacific Crest Trail have recently fallen ill. The Pacific Crest Trail Association (PCTA) confirmed reports that at least two dozen hikers near Wrightwood, in the San Gabriel Mountains of San Bernardino County, have contracted norovirus.
The outbreak has been severe enough to prompt at least one air rescue. On May 20, the PCTA posted on Instagram acknowledging the gastrointestinal illness reports and announced their collaboration with the San Bernardino County Department of Public Health to monitor the situation closely.
Nationwide data indicates a growing presence of norovirus. NBC News highlighted that wastewater surveillance points to increasing “high” norovirus levels in parts of the country, particularly in the Northeast. According to the Centers for Disease Control and Prevention (CDC), there were 1,194 suspected or confirmed norovirus outbreaks between August 1, 2025, and May 7, 2026, aligning with average outbreak figures from previous years.
Stanford-led WastewaterSCAN, a national infectious disease monitoring project, reported a medium level of norovirus concentration across the U.S. as of June 1, down slightly from a “high” alert in late May. Currently, 50 locations nationwide-including cities such as Las Vegas, Boston, and Memphis-are experiencing elevated norovirus activity.
Dr. Linda Yancey, an infectious disease expert at Memorial Hermann, noted a localized norovirus outbreak in the San Francisco Bay Area but emphasized that overall national levels remain typical for this time of year.
“There really isn’t anything unusual about this one in California,” she explained. “They just got unlucky.”
Norovirus, which causes acute gastroenteritis (inflammation of the stomach and intestines), is distinct from the flu virus. It spreads rapidly through direct contact with infected individuals, consumption of contaminated food or drink, or touching contaminated surfaces and then one’s mouth. While symptoms such as diarrhea, vomiting, nausea, and stomach pain typically resolve within one to three days, infected individuals can still transmit the virus for up to two weeks after recovery.
To reduce the risk of infection, health experts recommend frequent and thorough handwashing with soap and water, avoiding potentially contaminated food and water, disinfecting surfaces regularly, and practicing caution when traveling. The CDC also advises washing laundry in hot water and staying home for at least two days after symptoms subside to prevent further spread.
With norovirus activity rising in some areas, awareness and preventive measures remain critical to protecting public health during the summer months.