Norovirus is surging in the US: What do we need to know? | Health News

Norovirus is spreading across the United States this winter. Also referred to as the “winter vomiting bug,” norovirus is a highly contagious virus that spreads through contaminated surfaces, food, water, and close contact with infected individuals.

Here’s what to know about the virus, how it spreads, and the current outbreak in the United States.

What is norovirus?

Norovirus is the cause of 58 percent of foodborne illnesses in the United States.

It is sometimes known as Norwalk virus, named after the first strain of Norwalk virus norovirus Set in Norwalk, Ohio in the 1970s.

Norovirus belongs to a family of small RNA viruses called caliciviruses, which cause infections in their hosts, including humans and animals such as pigs, cows, rabbits and dogs.

Norovirus outbreaks are most prevalent between November and April, a period often referred to as “norovirus season.”

How does norovirus spread?

Norovirus is highly contagious. It is spread by direct contact with virus particles found on surfaces and people, by consuming contaminated liquids and foods, by aerosols and not washing hands properly.

Transfer occurs in several ways. Infection can occur when people touch surfaces containing norovirus particles or individuals infected with the virus then touch their mouth, nose, or eyes. The virus is also transmitted by drinking fluids or eating foods that contain norovirus particles.

Norovirus usually spreads when an infected person touches food, drinks, or ice before serving it, or when people share food or eating utensils or have close personal contact.

The virus targets the small intestine, where it multiplies and causes inflammation, leading to gastroenteritis, or intestinal dysfunction, leading to diarrhea and vomiting.

The virus is remarkably resilient and can survive on hard or soft surfaces – such as covers – and in various environments for up to two weeks, making it particularly difficult to contain.

Is norovirus airborne?

Norovirus is not an airborne virus like influenza or COVID-19. However, it can become an aerosol if an infected person vomits and small droplets containing the virus are released into the air. When inhaled, these drops can lead to infection.

Norovirus tends to spread quickly in confined spaces such as cruise ships, where many passengers gather in close quarters or enclosed spaces and eat dinner together.

Earlier this month, a norovirus outbreak on three separate cruise ships around Hawaii and the Caribbean left 301 passengers infected. This was the largest number of cruise ship outbreaks ever recorded in a single month.

Can you get norovirus from shellfish?

Raw or undercooked shellfish, especially oysters, are a well-documented carrier of norovirus.

Oysters feed themselves constantly by filtering their food from large amounts of water in a process known as “filter feeding.” During this process, they can pick up contaminants such as norovirus from contaminated water. Because norovirus is highly contagious, even small particles in water can carry enough virus to cause illness.

The U.S. Food and Drug Administration (FDA) has issued a warning against the consumption or sale of oysters from specific harvest periods and companies in British Columbia, Canada due to their potential norovirus contamination. This advisory applies to restaurants, retailers and consumers.

In 2022, outbreaks in several states in the United States were linked to raw oysters harvested from Texas waters. In 2023, several norovirus outbreaks in Europe were traced to shellfish.

A senior scientist at the US Centers for Disease Control and Prevention said that while news reports often focus on infections caused by shellfish, at least 80 percent of cases are transmitted through personal contact.

“Eating raw seafood always poses a risk of gastrointestinal (gut-related) infections such as norovirus, but compared to the total number of foodborne cases, shellfish-related outbreaks make up a small percentage,” he told Al Jazeera via email. His identity remains anonymous because he is not authorized to speak to the media.

How big is the current outbreak in the United States?

This winter, the United States is seeing a spike in norovirus cases.

According to data from the US Centers for Disease Control and Prevention, the number of outbreaks rose from 69 in the last week of November, to 91 in the first week of December. Previously, the highest number of outbreaks over a one-week period in the same time frame was 65, in 2019.

A norovirus “outbreak” is defined as two or more cases of illness associated with a common source, such as contaminated food or close contact in a particular environment. Outbreaks refer to clusters of infections, not individual cases.

In December, the Minnesota Department of Health recorded 40 norovirus cases, double the typical number for that month.

While norovirus cases typically spike in the United States during this time of year, a relatively new strain, GII.17, has become the dominant type this season, the Centers for Disease Control and Prevention scientist said.

He explained that lower population immunity to GII.17 compared to the previously dominant strain, GII.4 Sydney, may have contributed to an early increase in cases in December, rather than the usual increase in January.

What are the symptoms of norovirus?

The typical incubation period for norovirus is 12-24 hours, however, it can occur as quickly as 10 hours after exposure. Characteristic symptoms are sudden onset, vomiting and severe diarrhea. These symptoms can last from 24 to 36 hours.

The resulting dehydration is a serious concern, especially for young children, the elderly, and individuals with weakened immune systems.

Young children have lower fluid reserves, and older people or those with chronic diseases may find it more difficult to tolerate rapid fluid loss.

Signs of dehydration include dry mouth, decreased urination, and dizziness, as well as unusual sleepiness in children.

Other symptoms include:

• nausea
• Abdominal pain
• Body aches, headache
• Low grade fever

Most people recover completely within a few days.

How is norovirus treated?

Norovirus cannot be treated with medication; it needs to run its course. The primary focus is on managing symptoms, especially dehydration by drinking plenty of fluids, such as water or oral rehydration solutions.

Drinks such as coffee, tea and alcohol can worsen dehydration and should be avoided.

In the case of severe dehydration, medical intervention, such as intravenous fluids, may be needed. Some doctors may also prescribe over-the-counter antidiarrheal medications.

How to prevent norovirus infection?

The CDC recommends several measures to prevent norovirus infection:

• Practice strict hygiene: Wash hands frequently with soap and warm water for at least 20 seconds, especially before eating and after using the bathroom.
• Surface disinfection: Use household cleaning solutions specifically designed to kill viruses, paying close attention to frequently touched areas such as doorknobs and countertops.
• Stay at home: While symptoms are present, avoid preparing food for others. Stay home for at least two days after symptoms disappear.
• Food safety practice: Cook food well and wash hands frequently. Avoid eating raw shellfish, which can sometimes harbor the virus.
• Avoid relying on hand sanitizers: Alcohol-based hand sanitizers are less effective against norovirus and should not be used as a substitute for proper hand washing.