The “Ferrari of viruses” is having a banner season. Norovirus, which races through cruise ships, homes, and long-term care facilities, is experiencing a remarkable winter surge in the Northern Hemisphere, sending large numbers of people racing to the bathroom and many others to the hospital, and in rare cases proving fatal.”
Jon Cohen, writer and correspondent, Science
Publilius Syrus, Latin writer, 1st century, BCE
Norovirus is the number one cause of acute gastroenteritis in the world killing an estimated 200,000 young children each year. In the U.S., it is the leading cause of hospitalizations due to diarrheal disease. On January 14, 2025, the Centers for Disease Control and Prevention (CDC) reported this winter’s wave of norovirus infections reached levels that are more than double last year’s season peak. Hence, I thought it would be a good time to discuss why this is happening and to refresh your memory about how to prevent this gastrointestinal tract infection.
Norovirus gastroenteritis: a recap. Gastroenteritis or acute diarrheal disease is surprisingly common. It’s estimated that the average adult has an episode of diarrhea—defined as three or more loose stools per day—about four times a year. A large repertoire of pathogens including viruses, bacteria, and parasites are responsible for causing gastroenteritis. Norovirus is one of these pathogens. And because norovirus is so incredibly contagious, it reigns supreme. As a cause of gastroenteritis, it is “public enemy number 1.”
Norovirus disease is sometimes referred to as the “stomach bug” or “stomach flu.” As most cases occur between November and April and as vomiting is often a prominent symptom, especially in adults, it also goes by the name “winter vomiting disease.” (See, “Outbreaks of ‘Winter Vomiting Disease’ (Norovirus Infection) Are on the Rise,” Germ Gems, March 1, 2023.)
In 1972, National Institutes of Health scientist Albert Kapikian first identified the prototype norovirus—a RNA virus—in a stool specimen from an outbreak of gastroenteritis that erupted in an elementary school in Norwalk, Ohio in 1968. (Early on, the virus was named “Norwalk virus” which was shortened later to norovirus.) It became clear after genomic testing that norovirus evolves rapidly. Currently, there are 29 different known strains, and each strain has different variants. The recent surge in norovirus cases appears to be due to a newly evolved variant designated G11.17.
Epidemiology. In the U.S. alone, noroviruses are estimated to cause 21 million illnesses each year and to contribute to some 70,000 hospitalizations and 800 deaths. Of the estimated 212,000 deaths globally per year, 99% occur in the developing world. Noroviruses are a very common threat in daycare centers, in nursing homes and on cruise ships. The very young and the elderly are at greatest risk of severe disease and mortality.
Noroviruses are the leading cause of foodborne disease. (Leafy greens, fresh fruit, and shellfish are the most commonly involved.) Hands or food contaminated with fecal matter are the primary modes of transmission of noroviruses.
Clinical features. Diarrhea, nausea, vomiting, abdominal pain, fever, headache, and body aches are the most common symptoms of norovirus disease. Most symptoms develop 12 to 48 hours after exposure to norovirus. Signs of life-threatening infection are dehydration, bloody stools, high fever and severe abdominal pain. If one develops any of these life-threatening symptoms, promptly seek medical attention.
Treatment. There is no specific antiviral therapy for norovirus infection. Drinking plenty of water is, however, crucial. And, in severe cases, rehydration can be life-saving.
Prevention. At present, there is no vaccine against norovirus. Some vaccines are being developed, but recently, one promising candidate was found ineffective in a clinical trial.
Proper handwashing with soap and water is therefore the mainstay of preventing norovirus infection. (According to the CDC, alcohol-based hand sanitizers are ineffective against norovirus, due to its firm protein shell.) Disinfecting kitchen surfaces, washing fruits and vegetables, and cooking seafood to at least 63C (145F) are other important measures.
In April, 2024, the CDC launched “Life is Better with Clean Hands,” a national campaign encouraging adults to make clean hands part of their daily lives, especially before cooking or after using the bathroom. To learn how to clean one’s hands properly, all adults and children should view (and review) the CDC’s You Tube video, “Fight Germs: Wash Your Hands.” It is excellent. And during this current surge in norovirus infections, it is hands down worth the time.
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