Norovirus Vomiting Virus 2026 Spreads Across U.S. as Wastewater Levels Reach High Alert

A highly contagious stomach illness known as norovirus is spreading across the United States at elevated levels, with wastewater surveillance systems detecting high concentrations across multiple regions. Recent outbreaks have struck outdoor enthusiasts along the Pacific Crest Trail in Southern California, prompting health alerts from hiking organizations and local authorities. The virus, commonly called the "winter vomiting disease," continues to circulate well into spring months, affecting both recreational areas and communities nationwide.

Current Outbreak Activity

The Pacific Crest Trail Association confirmed reports of gastrointestinal illness affecting hikers in the Wrightwood area of San Bernardino County, California. At least two dozen hikers fell ill over a two-week period, with cases requiring urgent care visits in Hesperia and Victorville, where medical staff confirmed norovirus diagnoses. The outbreak prompted at least one air rescue operation and has sparked health precautions in rural communities along the trail corridor, which extends through the San Gabriel Mountains, Cajon Pass, Big Bear, and into Riverside County.

WastewaterSCAN, an academic surveillance program operated through Stanford University in partnership with Emory University, reports that norovirus remains in the "high" category nationwide based on high concentrations detected over the previous 21 days. Rates are currently rising in the Northeast region. According to the CDC's NoroSTAT program, 1,194 outbreaks were recorded from August 1 through May 7 of the current period, compared with 2,534 during the same timeframe the previous year—a figure consistent with historical averages.

Dominant Strains and Symptoms

Two primary norovirus strains are currently circulating: GII.4, a strain that has circulated for years, and GII.17, a newer mutated variant that partially evades prior immunity. During the 2024–25 season, GII.17 became the predominant strain in the United States, accounting for approximately 75 percent of outbreaks. Despite genetic differences, both variants produce similar symptoms including vomiting, diarrhea, nausea, and stomach cramps.

Norovirus spreads rapidly between people in close quarters and has historically caused outbreaks at schools, shelters, camps, hospitals, nursing homes, and cruise ships. Previous trail-related outbreaks occurred on the 2,200-mile Appalachian Trail last summer and at Grand Canyon National Park in 2022, when at least 222 people became infected. The Pacific Crest Trail's nearly 2,650-mile route from Mexico to Canada presents particular transmission risks, as thru-hikers spend approximately five months in close proximity at shelters and water sources.

Prevention and Treatment

Health officials recommend that infected individuals drink plenty of fluids and wash hands frequently. Medical treatment is advised for those experiencing dehydration or illness lasting more than a few days. While most people recover at home without professional medical intervention, comprehensive clinical data on norovirus outbreaks remains limited because the majority of cases are not formally reported through healthcare systems.