Flu season may be winding down. However, recent reports from Southern California indicate that norovirus remains a concern, especially following outbreaks impacting hikers.
The NBC reports that the recent wastewater surveillance has revealed high levels of norovirus across much of the country. WastewaterSCAN scientific program manager Amanda Bidwell said that norovirus levels have remained elevated for the past 21 days. According to the Centers for Disease Control and Prevention’s NoroSTAT program, there were 1,194 outbreaks recorded between Aug. 1, 2025, and May 7, 2026. That figure is actually down from 2,534 outbreaks during the same period ending last year.
Norovirus is colloquially referred to as the “winter vomiting disease.” According to Bidwell, the unusual aspect is not necessarily the outbreak itself, but the fact that outbreaks are continuing this late into spring. An infectious disease specialist at Houston’s Memorial Hermann, Linda Yancey, also added context to the discussion, saying there is nothing particularly unusual about the outbreak rate itself. Dr. Yancey notes that California simply got “unlucky.”
Bidwell also pointed out the difficulties in accurately tracking every outbreak, since the CDC can only account for confirmed cases. Bidwell said, “Monitoring norovirus in wastewater is very helpful for this highly contagious virus, as there is not a lot of clinical data to describe outbreaks because most people recover at home without seeing a healthcare professional” (via NBC).
As the weather gets warmer, people are expected to spend more time hiking and traveling outdoors. And while that already comes with its own risks, this time the heat itself could become part of the issue. Scott Roberts of Yale School of Medicine predicted that holiday travel will lead to more social interaction, while rising temperatures may push people indoors into tighter spaces. According to Roberts, this could further accelerate viral transmission.
Dr. Yancey compared the “winter vomiting disease” to measles because of how extraordinarily contagious it is. It is common for one infected person to spread the illness to as many as seven others (via NBC).
Dr. Roberts also raised concerns that collective immunity may not provide much long-term protection. He reportedly said, “I have not seen any evidence of a new strain, but as with all viruses, evolution occurs, and unfortunately, our immunity to norovirus is not long-lasting.”
Norovirus remains the most common known cause of food poisoning in the United States. For people to better recognize when they may need medical attention, it is also important to understand the symptoms associated with the illness. Symptoms include stomach pain, nausea, vomiting, and diarrhea. More severe cases may also involve headaches, fever, and body aches. These symptoms usually begin appearing between 12 and 48 hours after infection (via National Institutes of Health).
Reportedly, hand sanitizers are also often ineffective against the virus. The best protection is to thoroughly wash your hands with soap and water, regardless of whether you have used sanitizer throughout the day. It may also help to avoid shellfish.
