If it seems as though everyone you know is coming down with a stomach bug, it’s not all in your head.
Rates of norovirus – commonly known as the stomach flu – are roughly twice as high as they were from 2021 to 2024 and nine times higher than during the first year of the pandemic.
There were 91 outbreaks of the virus during the week ending December 5, the most recent date with available data, and state-level trends suggest that this number will continue to rise.
This time last year, health departments across more than a dozen states reported just 41 outbreaks.
And during the Covid pandemic, the CDC reported no more than 10 outbreak per week, which infectious disease experts attribute to masking, social distancing, isolation, and frequent hand washing.
Norovirus causes severe diarrhea and vomiting, which can lead to life-threatening dehydration. It spreads through contact with germs from an infected person’s vomit or feces, contaminated food, shared utensils, or surfaces they’ve touched.
The virus infects around 21 million Americans annually and sends around 2 million to their doctor’s offices or urgent care.
While most people recover within a few days, the virus kills around 900 people every year, mostly adults 65 and up.
Outbreaks are most common around this time of year due to a jump in the number of people gathering in groups for holiday festivities, traveling, and staying warm indoors, where pathogens can spread easily.
This year’s meteoric rise could also be attributed to pandemic-era safety measures, such as the widespread use of hand sanitizers, masking, and isolation.
Norovirus immunity remains strong for just a few years, so by the time society nixed those safety precautions, population-wide immunity had dissipated.
The CDC’s latest figures support this theory. From 2012 to 2020, the US documented around 1,500 norovirus outbreaks; in the subsequent five years, there were nearly 2,400 outbreaks. Over 400 were recorded in 2024 alone.
Hand washing can make the difference between normal health and a sleepless night hunched over the toilet.
Dr Celine Gounder, an infectious disease specialist at New York University’s Grossman School of Medicine, told NPR: ‘We did see gastroenteritis of different kinds go down during the pandemic because people were also hand-washing.
‘And then, once there was a return to sort of more normal disgusting behavior, we saw it go up again.’
Doctors say illness can be avoided by thoroughly washing your hands with soap and water for at least 20 seconds, washing produce before eating it, sanitizing countertops, avoiding people who have been infected, and cooking seafood to at least 145 degrees.
Some scientists have speculated that this year’s flood of norovirus cases could be caused by a novel strain to which people have no pre-existing immunity.
Lee-Ann Jaykus, a microbiologist at North Carolina State University who directs NoroCORE, a food virology collaboration among multiple federal agencies, said that while the CDC’s genetic analyses of circulating noroviruses haven’t revealed any significant changes this season, the potential emergence of a new strain is a key concern for many experts.
She told Vox: ‘I can guarantee you that my colleagues at the CDC are doing a lot of sequencing now to figure out if there is a new strain, but it’s too early to say that there is.’
Symptoms of norovirus – nausea, vomiting, and diarrhea – come on quickly, within 12 to 48 hours of exposure.
Dehydration is a major concern. Frequent vomiting and diarrhea can quickly cause the body to lose fluids and electrolytes, which can lead to dangerously low blood pressure, reduced blood flow to vital organs, and an electrolyte imbalance that may harm the heart and muscles.
Electrolyte imbalances can also result in seizures and, in some cases, loss of consciousness.
Hand sanitizers alone can’t kill virus particles on the skin, which is why doctors strongly recommend washing one’s hands often.
