Key Takeaways
-Over 20 hikers on Southern California’s Pacific Crest Trail have fallen ill with norovirus, prompting at least one air rescue.
- Nationwide wastewater monitoring shows high and rising norovirus activity, especially in the Northeast and Midwest.
- Recent CDC data confirms a multi‑week surge in cases following the typical winter decline.
- Late‑spring spikes are expected; the virus peaks in early March and tapers in spring.
- Wastewater testing often captures infections missed by clinical reporting, suggesting true case numbers may be higher.
- The novel GII.17 strain now accounts for ~75 % of outbreaks, potentially driving recent surges due to limited population immunity.
- Norovirus causes sudden vomiting, diarrhea, and dehydration, spreads easily, and can survive harsh conditions, making hand hygiene the primary defense.
Hiker Outbreak in the San Gabriel Mountains
At least two dozen hikers trekking the Pacific Crest Trail near Wrightwood in the San Gabriel Mountains of San Bernardino County have been stricken with a rapidly spreading norovirus outbreak over the past two weeks. Symptoms of vomiting and diarrhea were severe enough to require one air‑medical evacuation, underscoring how quickly the illness can incapacitate people in remote settings.
National Wastewater Data Highlights Surge
Data from the WastewaterSCAN project, which samples sewage across the United States, classified norovirus activity as “high” and trending upward in late May. More than 100 % of the samples tested positive, with particularly sharp increases observed in the Northeast and Midwest, indicating that the virus is circulating broadly at a national level.
CDC Confirms Multi‑Week Increase in Cases
According to the National Respiratory and Enteric Virus Surveillance System, the proportion of norovirus tests that came back positive rose from 11.2 % (week ending April 28) to 12 % (week ending May 2). This follows a steep decline that began in March, marking the start of a new upswing that health officials say aligns with expected seasonal patterns.
Seasonal Expectations and Typical Peaks
Norovirus is classically associated with cold‑weather months—roughly November through April—when colds and flu are most common. However, late‑spring surges are not unusual; the virus often begins to climb in late fall, peaks in early March, and tapers off during the spring, as explained by researchers in the field.
Wastewater Surveillance Reveals Under‑Reported Cases The CDC’s NoroSTAT program records only confirmed cases from participating state health departments, which can miss many infections that resolve at home without medical attention. Wastewater data therefore provides a more comprehensive snapshot of the true prevalence, especially since most people shed the virus in their stool long after symptoms subside.
Dominant Norovirus Strains and Emerging Variants
Two genotypes, GII.4 and GII.17, currently dominate the circulating strains. While GII.4 was historically the most prevalent, the more mutated GII.17 overtook it during the 2024‑2025 season, accounting for roughly 75 % of cases. This shift may be contributing to the recent uptick, particularly because many communities have limited immunity to the newer variant.
What Is Norovirus and How Does It Present?
Norovirus is a highly contagious pathogen that causes acute gastroenteritis, commonly known as the “stomach bug.” Typical symptoms include sudden nausea, vomiting, diarrhea, abdominal cramping, and sometimes fever, headache, or body aches. Dehydration is a major concern, with signs such as dark urine, dry mouth, and dizziness. The illness usually lasts one to three days, though viral shedding can continue in stool for several weeks.
Prevention and Control Recommendations
Because norovirus resists many common disinfectants and survives both heat and cold, prevention focuses on rigorous hand hygiene: wash hands with hot, soapy water for at least 20 seconds before eating, after using the restroom, and after handling food. Additionally, thoroughly cook foods, clean and sanitize contaminated surfaces, and wash fruits and vegetables before consumption to reduce the risk of infection.