Norovirus is a highly contagious virus that causes acute gastroenteritis, an inflammation of the stomach and intestines. It is commonly referred to as “stomach flu” or “stomach bug,” but it is not related to the influenza virus that causes respiratory illness. Norovirus is a pathogenic human virus, recognized as the leading cause of vomiting, diarrhea, and foodborne illness in the United States. This widespread pathogen affects an estimated 19 to 21 million individuals annually.
Understanding Norovirus Illness
Norovirus infection leads to a range of symptoms. Individuals experience nausea, vomiting, stomach pain or cramps, and watery diarrhea. Other symptoms can include a low-grade fever, headache, body aches, and a general feeling of illness.
Symptoms appear within 12 to 48 hours after exposure to the virus. The illness is brief, with symptoms lasting for 1 to 3 days. Severity can lead to approximately 109,000 hospitalizations and 900 deaths each year in the United States, predominantly among adults aged 65 and older. The virus directly infects cells lining the gastrointestinal tract, causing inflammation and injury to the intestinal villi. This impairs fluid absorption and can lead to significant fluid loss through watery diarrhea, resulting in dehydration, especially in young children, older adults, and those with other underlying health conditions.
How Norovirus Spreads
Norovirus is highly contagious. The virus is present in the stool and vomit of infected individuals, even before symptoms begin. Transmission occurs primarily through the fecal-oral route, meaning accidental ingestion of tiny particles of feces or vomit from an infected person.
Transmission occurs through direct contact with an infected individual, such as caring for someone who is sick, or through consuming contaminated food or water. Food can become contaminated if handled by an infected person with unwashed hands, or if it comes into contact with virus particles. Water sources, including recreational or drinking water, can become contaminated if sewage leaks into wells or if water is not properly treated. Touching contaminated surfaces or objects and then touching one’s mouth is another mode of transmission, as noroviruses can survive on surfaces for days or even weeks. Individuals are most contagious when they have symptoms and for at least three days after recovery, with some remaining contagious for up to two weeks.
Managing and Preventing Norovirus
There is no specific medicine available to treat norovirus infection. Antibiotics are ineffective because they target bacteria, not viruses. Management of norovirus illness focuses on supportive care, primarily preventing dehydration by drinking plenty of liquids. Oral rehydration solutions are recommended to replace lost fluids and electrolytes, especially for vulnerable populations such as young children and older adults. In cases of severe dehydration, intravenous fluid rehydration may be necessary, sometimes requiring hospital admission.
Preventing the spread of norovirus involves hygiene practices. Thorough handwashing with soap and water for at least 20 seconds is highly effective, as alcohol-based hand sanitizers are less effective against norovirus. Proper food handling is also important; this includes washing fruits and vegetables thoroughly and cooking shellfish, such as oysters, completely to kill the virus. Cleaning and disinfecting contaminated surfaces with a bleach-based solution is recommended after someone has vomited or had diarrhea. An EPA-registered disinfectant effective against norovirus should be used, ensuring the surface remains wet for at least 5 minutes.
The Broader Impact of Norovirus
Norovirus encompasses many different types, with Genogroups I, II, and IV being the primary human pathogens. Infection with one type does not guarantee protection against others, which explains why individuals can experience multiple norovirus infections throughout their lifetime. The most common human norovirus genotype, GII.4, undergoes antigenic changes, leading to the emergence of new strains every two to four years, which can result in increased cases and global outbreaks.
The virus places a burden on public health and healthcare systems. Norovirus is the most frequent cause of outbreaks of hospital-acquired infection, accounting for a large percentage of hospital unit closures. Outbreaks frequently occur in various communal settings, including healthcare facilities, schools, and cruise ships, where close quarters facilitate rapid transmission. While vaccines are currently under research and development, they are not yet widely available. The diversity and rapid evolution of norovirus strains present challenges for vaccine development, but continued efforts aim to reduce the disease burden.