Norovirus can cause nausea, vomiting and diarrhea and is highly transmissible.

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Nearly 100 passengers and crew aboard Royal Caribbean’s Serenade of the Seas recently contracted norovirus during a 13-day cruise from San Diego to Miami. This outbreak highlights the persistent challenge this highly contagious virus poses in close-quarter settings. As winter approaches, understanding norovirus—its transmission, symptoms, and prevention—is more important than ever.

What is Norovirus and How Does It Spread?

Norovirus is a viral infection that causes acute gastroenteritis, or inflammation of the stomach and intestines. Although it is commonly referred to as the “stomach flu”, it is unrelated to influenza virus. Norovirus is the leading cause of foodborne illness in the United States, causing roughly 19 to 21 million cases annually according to the Centers for Disease Control and Prevention.

The virus is highly infectious and can be spread through multiple routes. People can become infected by consuming contaminated food or water, particularly shellfish or fresh produce handled by infected food workers. Direct person-to-person transmission can occur when an infected individual shakes hands or cares for someone else. Additionally, the virus can spread indirectly by touching contaminated surfaces and then touching your eyes, nose or mouth. Norovirus outbreaks are most common during the winter months, between November and April in the United States.

Norovirus can persist on surfaces for days or even weeks, and it may require exposure to less than 100 viral particles to cause infection. Infected individuals can shed millions of viral particles in their stool and vomit and may remain contagious for at least two to three days after symptoms resolve.

Disease Caused by Norovirus

Following infection, norovirus can rapidly cause disease. Symptoms typically appear 12 to 48 hours after exposure and include sudden onset of nausea, vomiting, watery diarrhea, and abdominal cramping. Infected individuals may also experience a low-grade fever, headache, body aches, and fatigue.

Fortunately, the illness is usually self-limiting, with symptoms lasting one to three days in most healthy adults. However, fluid loss from vomiting and diarrhea can quickly lead to dehydration, which is the most serious complication. Warning signs include decreased urination, dry mouth and throat, dizziness when standing, and in children, unusual sleepiness or fussiness.

Certain populations face higher risks from norovirus infection. Young children, older adults, pregnant women, and those with a weakened immune system are more vulnerable to severe dehydration and may require medical attention or hospitalization.

Is Testing Needed for Norovirus?

Healthcare providers typically diagnose norovirus based on symptoms and known outbreaks in the community. However, laboratory confirmation is available and may be used during outbreak investigations, in hospital settings, or in those with severe disease.

The most common and reliable test is a molecular, or PCR assay, performed on stool samples. Molecular tests can detect norovirus genetic material with high sensitivity and can provide results the same day the sample is received in a lab. In outbreak settings, including aboard cruise ships, antigen tests are often used. These tests look for viral proteins in a person’s stool sample and can often generate results within 15-20 minutes.

For most individual cases, testing isn’t necessary since treatment is limited to supportive care and maintaining hydration. However, testing can be important during outbreak investigations to identify the source, implement appropriate control measures, and track the spread within communities or settings like cruise ships, nursing homes, or schools.

How Can You Avoid Being Infected with Norovirus?

Since there is no vaccine or specific antiviral treatment for norovirus, prevention is key. The most effective defense is good hand hygiene. Wash your hands thoroughly with soap and water, especially after using the bathroom, changing diapers, and before preparing or eating food. Importantly, alcohol-based hand sanitizers are not effective against norovirus.

When it comes to food safety, cook shellfish thoroughly, wash fruits and vegetables carefully, and avoid preparing food for others when you’re sick. If someone in your household experiences vomiting and diarrhea, disinfect contaminated surfaces immediately using a bleach-based cleaner, as common household cleaners may not effectively inactivate norovirus.

In outbreak situations, isolating sick individuals, enhancing cleaning protocols, and promptly reporting illnesses to health authorities are critical steps. If you become infected, stay home from work or school, avoid preparing food for others, and stay hydrated by drinking plenty of water or clear liquids.

Norovirus is an extremely contagious viral infection that causes an unpleasant illness. Knowing how the virus is spread and what you can do to reduce the chances of becoming infected can help keep you healthy this upcoming winter.