The Norwalk virus, now commonly referred to as norovirus, represents a highly contagious group of viruses. It causes gastroenteritis, which is an inflammation of the stomach and intestines. This infection is a frequent cause of sudden vomiting and diarrhea in people of all ages. Norovirus is the leading cause of foodborne illness in the United States, with millions of cases reported annually. While often called the “stomach flu,” norovirus is not related to the influenza virus, which causes respiratory illness.
Symptoms and Course of Illness
Norovirus infection manifests with sudden symptoms, including nausea, vomiting, watery diarrhea, and stomach cramps. Individuals may also experience a low-grade fever, headache, body aches, and tiredness. Symptoms usually occur within 12 to 48 hours after exposure.
The illness runs its course within 1 to 3 days, with most people recovering completely without specific medical treatment. While symptoms can be intense, the infection is self-limiting. Children may experience more vomiting, while adults often have more diarrhea.
How it Spreads
Norovirus is highly contagious, spreading primarily through the fecal-oral route. This means the virus transmits when tiny particles of feces or vomit from an infected person are accidentally ingested. As few as 10 to 100 viral particles can cause an infection.
The virus can spread through contaminated food and water. This occurs when an infected person touches food with unwashed hands, or when food is placed on contaminated surfaces. Certain foods, like raw shellfish (such as oysters) and produce, can become contaminated at their source if exposed to tainted water.
Person-to-person contact is another common transmission method, occurring through direct contact with an infected individual, such as caring for them or sharing eating utensils. Additionally, touching contaminated objects or surfaces and then touching one’s mouth can lead to infection. Infected individuals can be contagious from the moment they begin feeling ill and for at least 3 days after recovery, with some individuals shedding the virus for up to two weeks or even months in some cases, even without symptoms.
Managing the Illness and Preventing Spread
Managing norovirus illness focuses on supportive care to alleviate symptoms and prevent complications. Staying well-hydrated is important, as vomiting and diarrhea can lead to significant fluid loss. Drinking clear fluids such as water, oral rehydration solutions, and clear broths is recommended. Sugary drinks like sodas and some fruit juices should be avoided, as they can worsen diarrhea. Caffeine and alcohol should also be avoided.
Rest is also beneficial for recovery. When an individual can tolerate food, beginning with bland, easy-to-digest options like plain toast, rice, bananas, applesauce, or crackers can help. Eating small amounts frequently, rather than large meals, can be more manageable. Dairy products, fatty, or highly seasoned foods should be avoided for a few days.
Preventing the spread of norovirus requires hygiene practices. Thorough handwashing with soap and water for at least 20 seconds is the most effective way to remove virus particles, especially after using the bathroom, changing diapers, and before eating or preparing food. Alcohol-based hand sanitizers are less effective against norovirus because the virus has a protective capsule that alcohol cannot penetrate.
Cleaning and disinfecting contaminated surfaces immediately is also important. A bleach solution or an EPA-registered disinfectant effective against norovirus should be used. Contaminated clothing or linens should be removed carefully without shaking and washed with detergent in hot water at the maximum available cycle length, then machine dried at the highest heat setting. Individuals who are sick should avoid preparing food for others and refrain from close contact for at least 2 to 3 days after symptoms have resolved to minimize transmission risk.
When to Seek Medical Attention
While norovirus resolves on its own, certain signs indicate a need for medical attention. Dehydration is a primary concern, particularly in young children, older adults, and those with weakened immune systems. Signs of dehydration include:
Decreased urination
A dry mouth and throat
Dizziness upon standing
In infants, crying with few or no tears or unusual sleepiness or fussiness
Seeking medical help is also advised for severe symptoms, including:
Persistent vomiting lasting more than 24 hours
Bloody diarrhea or bleeding from the bottom
A high fever (above 102°F for adults or 100.4°F for children)
Severe abdominal pain
If an individual is unable to keep fluids down, intravenous fluids may be necessary.