Norovirus is on the rise in the United States this winter. Also called the “vomit monster of winter”, norovirus is a highly contagious virus that spreads through contaminated surfaces, food and water, and close contact with infected people.
Here's what you need to know about the virus, how it spreads and how it's spreading in the US.
What is norovirus?
Norovirus is responsible for 58 percent of foodborne illnesses in the US.
It is sometimes known as the Norwalk virus, which is called the first type of norovirus became known in Norwalk, Ohio in the 1970s.
Norovirus belongs to the family of small RNA viruses called Caliciviridae, which cause disease in their hosts, including humans and animals such as pigs, cows, rabbits and dogs.
Norovirus outbreaks occur most frequently 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 infected particles in human surfaces, drinking contaminated food and drink, and through inhalation and improper hand washing.
Transmission occurs in several ways. The disease can occur when people touch surfaces with norovirus particles or infected people and touch their mouth, nose or eyes. The virus is also spread by drinking or eating foods that contain norovirus particles.
Norovirus is spread when an infected person touches food, drinks or ice before serving, or when people share food or eating utensils or have close contact.
The virus enters the small intestine where it replicates and causes inflammation, which causes stomach infections, or interferes with bowel function, which causes diarrhea and vomiting.
The virus is incredibly hardy and can live on hard or soft surfaces – such as paper – and in different environments for up to two weeks, making it difficult to contain.
Is norovirus airborne?
Norovirus is not an airborne virus like the flu or COVID-19. However, it can become aerosolised when an infected person vomits and small droplets of the virus are released into the air. If ingested, these droplets can cause infection.
Norovirus tends to spread quickly in confined spaces such as cruise ships, where many passengers congregate in close quarters or enclosed spaces, and eat together.
Earlier this month, three Norovirus cruise ships around Hawaii and the Caribbean sickened 301 passengers. It was the highest number of cruise ship cases in one month.
Can you get norovirus from oysters?
Raw or undercooked shellfish, especially oysters, are well-documented carriers of norovirus.
Oysters always feed themselves by filtering their food from the water in a process called “filter feeding”. During this time, they can pick up germs like norovirus from contaminated water. Because norovirus is highly contagious, even small particles in water can carry the virus.
The US Food and Drug Administration (FDA) has issued an advisory banning the consumption or sale of oysters from harvest and industry in British Columbia, Canada due to norovirus contamination. These guidelines apply to restaurants, retailers, and consumers.
In 2022, an international outbreak in the US was linked to raw oysters harvested in Texas waters. In 2023, several norovirus outbreaks in Europe were traced to oysters.
A senior scientist at the US Centers for Disease Control and Prevention said that while most reports are about oyster-related illnesses, about 80 percent of cases are spread through person-to-person contact.
“Eating raw fish is always a risk of intestinal-related diseases (intestinal-related) such as norovirus, but compared to the number of food-related epidemics, oyster-related epidemics make up a small part”, he told Al Jazeera by email, requesting. anonymity because he was not allowed to speak to the media.
How big is the current US epidemic?
This winter, the US is facing a serious norovirus outbreak.
According to the US CDC, the number of infections increased from 69 in the last week of November, to 91 in the first week of December. Previously, the highest number of attacks in one week in the same period was 65, in 2019.
An “outbreak” of a single norovirus is defined as two or more related infections from a common source, such as contaminated food or close contact with a specific environment. Outbreaks refer to groups of diseases, not individual events.
In December, the Minnesota Department of Health recorded 40 norovirus cases — double the number for that month.
A CDC scientist said that although norovirus cases rise in the US this time of year, the new strain, GII.17, has been the biggest strain this season.
The decrease in public safety at GII.17 compared to the previous crisis, GII.4 Sydney, may have contributed to the initial operation this December, not the increase in January, he explained.
What are the symptoms of norovirus?
The incubation period for norovirus is 12-24 hours, however, it can occur as quickly as 10 hours after exposure. Symptoms start suddenly and include severe vomiting and diarrhea. These symptoms last 24 to 36 hours.
Dehydration is a serious problem, especially for young children, adults and people with weakened immune systems.
Young children have limited fluid reserves, and older adults or those with chronic medical conditions may have difficulty tolerating rapid dehydration.
Symptoms of dehydration include dry mouth, decreased urination and dizziness, and sleepiness in children.
Other symptoms include:
- Nausea
- Abdominal pain
- Body ache, headache
- Average temperature
Most people recover within a few days.
How is norovirus treated?
Norovirus cannot be treated with drugs – it has to run its course. The main goal is to control 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 severe dehydration occurs, medical treatment, such as intravenous fluids, may be needed. Some doctors may also prescribe over-the-counter anti-diarrhea medications.
How to prevent norovirus infection?
The CDC recommends several ways to prevent norovirus infection:
- Be very clean: Wash your hands frequently with soap and warm water for at least 20 seconds, especially before eating and after using the bathroom.
- For disinfection: Use household cleaning products designed to kill viruses, focusing on high-touch surfaces such as doorknobs and countertops.
- Stay at home: Even with symptoms, avoid cooking food for others. Stay at home for at least two days after symptoms disappear.
- Try to protect foods: Cook food properly and wash your hands often. Avoid eating raw shellfish, which can sometimes be contaminated.
- Avoid relying on hand sanitizers: Alcohol-based hand sanitizers are ineffective against norovirus and should not be used in place of proper hand washing.