Norovirus is a highly contagious virus that commonly causes acute gastroenteritis, an inflammation of the stomach and intestines. This illness is often referred to as the “stomach bug” or “winter vomiting bug” due to its prevalence during colder months and its characteristic symptoms. It affects millions globally across all age groups. While generally not life-threatening, it can be severe in young children, older adults, and those with weakened immune systems.
The Norovirus Particle
The norovirus is not a true cell but rather a microscopic viral particle. It is classified as a small, non-enveloped RNA virus, meaning it lacks an outer lipid membrane. This absence of an outer envelope contributes to its resilience and ability to survive in various environmental conditions.
The genetic material of the norovirus consists of a single-stranded RNA genome. This genetic information is encased within a tough, protective protein shell called a capsid. The capsid is composed of a single major protein, viral protein 1 (VP1). This protein is divided into a shell (S) domain, which forms the core around the RNA, and a protruding (P) domain that extends from the surface. The P domain is further subdivided into P1 and P2 subdomains, with the P2 subdomain containing sites that bind to specific carbohydrates on human cell surfaces.
How Norovirus Invades and Multiplies
Norovirus infection begins when viral particles are ingested, often through contaminated food, water, or surfaces. Once inside the body, the virus travels to the small intestine, its primary target for replication.
Upon reaching the intestinal epithelial cells, the norovirus utilizes its P2 domain to bind to specific carbohydrates, known as histo-blood group antigens (HBGAs), present on the surface of these cells. This binding facilitates the entry of the virus into the host cell. Once inside, the virus takes over the cell’s internal machinery, reprogramming it to produce many copies of its own genetic material and proteins. This replication process leads to the formation of new viral particles, which are then released from the infected cells, ready to infect other cells or spread to new hosts.
How Norovirus Spreads
Norovirus is highly contagious, and its spread is efficient due to the small number of viral particles needed to cause infection. Primary routes of transmission include direct contact with an infected individual, such as caring for someone who is sick. Indirect transmission also occurs through contact with contaminated food or water, or by touching contaminated surfaces and then touching one’s mouth.
Contaminated food can become a vehicle for norovirus when an infected person handles it without proper hygiene, or if food comes into contact with contaminated water or surfaces. Raw shellfish, particularly oysters, are a common source of infection because they can concentrate viral particles from contaminated water. Norovirus spreads easily in crowded environments like schools, childcare centers, nursing homes, and cruise ships, where close contact and shared surfaces facilitate rapid transmission. The virus can persist on surfaces for days or even weeks, further contributing to its widespread nature.
What Happens When You Get Norovirus
When a person contracts norovirus, symptoms appear suddenly, within 12 to 48 hours after exposure. Common symptoms include nausea, forceful vomiting, watery diarrhea, and stomach cramps. Other symptoms may include a low-grade fever, headache, and body aches.
The illness runs its course quickly, with symptoms lasting about 1 to 3 days. While most individuals recover completely without specific medical treatment, significant fluid loss from vomiting and diarrhea can lead to dehydration. Symptoms of dehydration include decreased urination, dry mouth and throat, and feeling dizzy when standing up. It is important to stay well-hydrated by drinking plenty of fluids, such as water or oral rehydration solutions, especially for young children and older adults who are more susceptible to severe dehydration.
Preventing Norovirus Infection
Preventing norovirus infection relies on diligent hygiene practices. Thorough handwashing with soap and water for at least 20 seconds is the most effective way to remove viral particles, especially after using the restroom or changing diapers, and before preparing or eating food. Alcohol-based hand sanitizers are less effective against norovirus compared to soap and water.
Food safety measures also play a role in prevention:
- Wash fruits and vegetables thoroughly.
- Cook shellfish thoroughly.
- Clean and disinfect kitchen utensils and surfaces regularly, keeping raw and cooked foods separate to prevent cross-contamination.
- If someone is sick, avoid preparing food for others for at least 48 hours after symptoms have resolved.
Cleaning and disinfecting contaminated surfaces immediately after an incidence of vomit or diarrhea is another preventative measure. Disposable gloves and paper towels should be used for cleanup, followed by disinfecting the area with a chlorine bleach solution or an EPA-registered disinfectant effective against norovirus. Contaminated clothing and linens should be washed with detergent and hot water, then machine dried at a high heat setting.