Norovirus is surging across the United States this winter. Norovirus, also known as “winter vomiting sickness,” is a highly contagious virus that is spread through contaminated surfaces, food and water, and close contact with infected people.

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

What is norovirus?

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

It is sometimes called norovirus, named after the first strain of the virus. norovirus Discovered in Norwalk, Ohio, in the 1970s.

Norovirus belongs to the family of picornaviruses in the Caliciviridae family and can cause infection in hosts including humans and animals such as pigs, cattle, rabbits and dogs.

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

How is norovirus spread?

Norovirus is highly contagious. It is spread through direct contact with viral particles on surfaces and people, consumption of contaminated liquids and foods, aerosols and lack of proper hand washing.

Transmission occurs in many ways. Infection occurs when people touch surfaces that contain norovirus particles or someone who is infected with the virus and then touch their mouth, nose, or eyes. The virus is also spread by drinking liquids or food that contain norovirus particles.

Norovirus is usually spread when an infected person touches food, drink, or ice before it is served, or when people share food or eating utensils or have close personal contact.

The virus targets the small intestine, where it replicates and causes inflammation, leading to gastroenteritis, or disruption of intestinal function, leading to diarrhea and vomiting.

The virus is extremely resilient and can remain on hard or soft surfaces, such as sheets, and in various environments for up to two weeks, making it particularly difficult to control.

Is norovirus spread through the air?

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

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

Earlier this month, norovirus outbreaks occurred on three cruise ships in Hawaii and the Caribbean, sickening 301 passengers. This is the highest number of cruise ship outbreaks in a single month on record.

Can you get norovirus from oysters?

Raw or undercooked shellfish, especially oysters, are carriers of norovirus.

Oysters continuously feed themselves by filtering food from large volumes of water, a process known as “filter feeding.” In the process, they can absorb contaminants such as norovirus from contaminated water. Because norovirus is so 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 certain harvest periods and companies in British Columbia, Canada, due to potential norovirus contamination. This advice applies to restaurants, retailers and consumers.

In 2022, a multi-state outbreak in the United States was linked to raw oysters harvested from Texas waters. In 2023, multiple norovirus outbreaks in Europe were traced to oysters.

A senior scientist at the U.S. Centers for Disease Control and Prevention said that while news reports often center on oyster infections, at least 80 percent of cases are spread through person-to-person contact.

“There is always a risk of enteric (gut-related) infections such as norovirus when eating raw seafood, but oyster-related outbreaks represent a small proportion compared to the total number of foodborne outbreaks,” he told Al Jazeera via email. spoke on condition of anonymity because he was not authorized to speak to the media.

How big is the current epidemic in the United States?

Norovirus cases have increased significantly in the United States this winter.

Data from the U.S. Centers for Disease Control and Prevention shows that the number of outbreaks surged from 69 in the last week of November to 91 in the first week of December. The previous highest number of outbreaks in a week during the same time period was 65 in 2019.

A single norovirus “outbreak” is defined as two or more related cases of illness that share a common source, such as contaminated food or close contact in a specific environment. An outbreak refers to a cluster of infections, not individual cases.

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

CDC scientists say that while norovirus cases in the United States typically rise this time of year, a relatively new strain, GII.17, has emerged as the dominant virus type this season.

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

What are the symptoms of norovirus?

The typical incubation period for norovirus is 12-24 hours, but it can occur as early as 10 hours after exposure. Its hallmark symptoms are sudden and severe vomiting and diarrhea. These symptoms can last 24 to 36 hours.

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

Young children have smaller fluid reserves, while older adults or those with chronic medical conditions may find it more challenging to tolerate rapid fluid loss.

Symptoms of dehydration include dry mouth, decreased urination, and dizziness, as well as atypical lethargy in children.

Other symptoms include:

• nausea
• stomach ache
• Body aches and headaches
• low fever

Most people fully recover within a few days.

How is norovirus treated?

Norovirus cannot be treated with medication – it needs to be allowed to take its course. The main focus is on controlling symptoms, especially dehydration by drinking plenty of fluids such as water or oral rehydration solutions.

Beverages such as coffee, tea and alcohol can increase dehydration and should be avoided.

If dehydration is severe, 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 steps to prevent norovirus infection:

• Practice strict hygiene habits: Wash your hands often with soap and warm water for at least 20 seconds, especially before eating and after using the bathroom.
• Disinfect surfaces: Use a home cleaning solution specifically designed to kill viruses and pay close attention to high-touch areas like doorknobs and countertops.
• Stay home: Avoid preparing food for others while you have symptoms. After symptoms subside, stay home for at least two days.
• Practice food safety: Cook food thoroughly and wash hands frequently. Avoid eating raw shellfish, which can sometimes carry viruses.
• Avoid relying on hand sanitizer: Alcohol-based hand sanitizers are less effective against norovirus and should not be used as a substitute for proper hand washing.