Norovirus (Stomach Flu): Symptoms, Treatment & Prevention

What Is Norovirus and What Causes It?

Norovirus is a highly contagious virus that infects the stomach and intestines, causing acute gastroenteritis with sudden onset of vomiting and diarrhea. It belongs to the Caliciviridae family and is the leading cause of foodborne illness outbreaks worldwide, responsible for approximately 685 million cases of acute gastroenteritis annually.

Norovirus, sometimes called the "winter vomiting bug" or stomach flu, is a group of viruses that cause inflammation of the stomach and intestinal lining. Despite the common name "stomach flu," norovirus is not related to influenza, which is a respiratory illness. The name "norovirus" comes from Norwalk, Ohio, where an outbreak in 1968 led to the virus's initial identification.

The virus is remarkably resilient and can survive on surfaces for days to weeks, making it particularly challenging to control. It remains stable in temperatures from freezing to 60°C (140°F) and is resistant to many common disinfectants, including alcohol-based hand sanitizers. This environmental persistence, combined with the extremely low infectious dose, explains why norovirus spreads so readily in communities, healthcare facilities, schools, and cruise ships.

There are many different genetic strains of norovirus, which is why people can become infected multiple times throughout their lives. Unlike some viral infections that confer lasting immunity, norovirus infection provides only temporary protection that lasts a few months at most. This genetic diversity also makes vaccine development challenging, though several candidates are currently in clinical trials.

How does norovirus spread?

Understanding transmission routes is essential for preventing norovirus spread. The virus is shed in enormous quantities in both vomit and feces of infected individuals, with peak viral shedding occurring during acute illness and for several days afterward. Remarkably, infected individuals can continue shedding virus particles for up to two weeks after symptoms resolve, which is why maintaining good hygiene during recovery is critical.

The main transmission routes include direct person-to-person contact, consumption of contaminated food or water, and touching contaminated surfaces followed by touching your mouth. Foodborne outbreaks often occur when food handlers who are infected prepare ready-to-eat foods. Shellfish, particularly oysters and other bivalve mollusks, can also accumulate norovirus from contaminated waters and cause illness when consumed raw or undercooked.

Aerosolized virus particles from vomiting can also lead to transmission, which is why outbreaks in enclosed spaces like cruise ships and healthcare facilities can spread so rapidly. Studies have documented that a single vomiting episode can create airborne droplets containing virus that settle on surrounding surfaces, potentially infecting people who weren't in direct contact with the ill person.

Who is most at risk from norovirus?

While norovirus can infect anyone regardless of age or health status, certain groups face higher risks of severe illness or complications. Young children under 5 years, adults over 65, pregnant women, and people with weakened immune systems are particularly vulnerable. In these populations, the fluid losses from vomiting and diarrhea can quickly lead to dangerous dehydration that may require medical intervention.

People living or working in closed or semi-closed environments face elevated infection risks due to increased opportunities for transmission. This includes residents and staff in nursing homes, patients in hospitals, military personnel in barracks, and travelers on cruise ships. Outbreaks in these settings can be particularly challenging to control and often require stringent infection control measures.

What Are the Symptoms of Norovirus?

The hallmark symptoms of norovirus are sudden, forceful vomiting and watery diarrhea that begin 12-48 hours after exposure. Most people also experience nausea, stomach cramps, low-grade fever, muscle aches, and fatigue. Symptoms typically last 1-3 days, though some people may feel unwell for up to a week.

Norovirus infection typically begins abruptly, often catching people by surprise. Many describe going from feeling perfectly normal to violently ill within just an hour or two. The sudden onset of symptoms is one of the distinguishing features of norovirus compared to other causes of gastroenteritis, which may have more gradual presentations.

Vomiting is often the first and most prominent symptom, particularly in children. The vomiting associated with norovirus is characteristically forceful, sometimes described as "projectile," and can occur multiple times per hour during the acute phase. While distressing, vomiting usually subsides within 24 hours, though it may persist longer in some individuals. Diarrhea typically accompanies or follows the vomiting and is watery, non-bloody, and may occur 4-8 or more times per day.

Beyond the gastrointestinal symptoms, norovirus infection commonly causes systemic effects including low-grade fever (usually below 38.9°C/102°F), headache, muscle aches and general malaise. These flu-like symptoms, combined with the gastrointestinal distress, contribute to the overall feeling of being quite unwell. Fortunately, these symptoms typically improve rapidly once the acute phase passes.

How are children's symptoms different?

Children, especially those under 5 years old, often experience more vomiting than diarrhea when infected with norovirus. This pattern is important for parents to recognize because frequent vomiting can quickly lead to dehydration in small children. The smaller body size of children means they have less fluid reserve and can become dehydrated faster than adults experiencing the same symptoms.

Watch for signs of dehydration in children including fewer wet diapers (less than 6 per day in infants), crying without tears, unusual drowsiness or irritability, and a dry mouth or tongue. A sunken soft spot (fontanelle) on an infant's head is a concerning sign of significant dehydration requiring immediate medical attention. Children may also refuse to drink, which creates a challenging cycle of fluid loss without replacement.

Symptoms in elderly and immunocompromised individuals

Older adults and those with compromised immune systems may experience more prolonged and severe symptoms. While healthy adults typically recover within 1-3 days, symptoms in these vulnerable groups can persist for 4-6 days or even longer. Additionally, immunocompromised individuals may shed virus for extended periods, sometimes weeks to months, potentially contributing to prolonged outbreaks in healthcare settings.

The risk of serious complications, particularly severe dehydration and electrolyte imbalances, is significantly higher in elderly individuals. Many older adults take medications that can compound the effects of dehydration, and pre-existing conditions like kidney disease or heart failure may be worsened by the fluid shifts that occur during acute gastroenteritis. Healthcare providers should maintain a low threshold for evaluation and treatment in these populations.

How Is Norovirus Treated?

There is no specific antiviral medication for norovirus. Treatment focuses on preventing dehydration through oral rehydration with water, electrolyte solutions, and clear fluids. Most people recover fully within 1-3 days with supportive care at home. Severe cases, particularly in young children, elderly, or immunocompromised individuals, may require intravenous fluids in a healthcare setting.

The foundation of norovirus treatment is fluid replacement. During the acute phase when vomiting and diarrhea are most severe, the body loses significant amounts of water and essential electrolytes including sodium, potassium, and chloride. Replacing these losses is critical because severe dehydration can lead to complications including kidney problems, confusion, and in extreme cases, cardiovascular collapse.

The most effective approach to fluid replacement involves small, frequent sips rather than large amounts at once. Drinking too much too quickly often triggers more vomiting, which is counterproductive. Start with small sips of water, clear broth, or oral rehydration solutions (ORS) every few minutes. Commercially available ORS products like Pedialyte or WHO oral rehydration salts provide an optimal balance of glucose and electrolytes to maximize fluid absorption in the intestines.

For children, continuing breastfeeding or formula feeding is recommended even during illness, as breast milk provides both nutrition and immune factors that may help recovery. Older children and adults can gradually advance to bland, easily digestible foods as symptoms improve. The traditional BRAT diet (bananas, rice, applesauce, toast) provides simple carbohydrates that are gentle on the recovering digestive system.

What should I eat and drink with norovirus?

During the acute phase of illness, most people find it difficult or impossible to eat, and that's perfectly acceptable. The priority is fluid intake, not food. However, once vomiting subsides, gradual reintroduction of food helps provide energy for recovery. Start with small amounts of bland foods and increase quantity and variety as tolerated.

Good fluid choices include water, oral rehydration solutions, clear broths, diluted apple juice, and sports drinks (though these contain more sugar than ORS). Avoid alcohol, caffeine, and highly sugary drinks as these can worsen diarrhea or interfere with fluid absorption. Similarly, carbonated beverages may contribute to nausea and should be avoided or allowed to go flat before drinking.

When ready to eat, start with bland, starchy foods that are easy to digest. Good options include plain crackers, white toast, plain rice, boiled potatoes, bananas, and plain pasta. Avoid dairy products, fatty or fried foods, spicy foods, raw vegetables, and high-fiber foods until fully recovered, as these can irritate the healing gut and prolong symptoms.

Medications for norovirus symptoms

While there's no cure for norovirus, certain over-the-counter medications may help manage symptoms in otherwise healthy adults. Anti-diarrheal medications like loperamide (Imodium) can reduce the frequency of bowel movements in adults, though they are not recommended for children or if there is bloody stool or high fever. These medications don't fight the infection but can provide symptomatic relief.

Anti-nausea medications (antiemetics) may be helpful for controlling severe nausea and vomiting. Ondansetron (Zofran) is sometimes prescribed, particularly for children, to help them tolerate oral fluids. However, medication use should be discussed with a healthcare provider, especially for young children, elderly individuals, or those with other health conditions.

Importantly, antibiotics are completely ineffective against norovirus because it's a viral infection, not bacterial. Taking antibiotics for viral gastroenteritis won't help and may actually harm by disrupting the beneficial bacteria in your gut and contributing to antibiotic resistance. Only take antibiotics if specifically prescribed by a healthcare provider for a confirmed bacterial infection.

When is hospital treatment needed?

Most cases of norovirus can be managed at home with supportive care, but some situations require medical evaluation and potentially hospital treatment. The primary concern is dehydration that cannot be corrected with oral fluids. If someone is unable to keep any fluids down for an extended period, or if signs of severe dehydration develop, intravenous (IV) fluid therapy may be necessary.

Hospital evaluation should be sought for infants and young children who are showing signs of dehydration, elderly individuals who appear confused or weak, anyone with underlying health conditions that could be complicated by dehydration, and people with severe symptoms that aren't improving after 3 days. In healthcare settings, IV fluids can quickly restore hydration and correct electrolyte imbalances.

When Should You See a Doctor for Norovirus?

Most healthy adults with norovirus don't need to see a doctor and recover fully at home. However, seek medical care if you show signs of severe dehydration, have bloody vomit or stool, experience severe abdominal pain, have symptoms lasting more than 3 days, or are unable to keep any fluids down for 24 hours. Young children, elderly people, pregnant women, and immunocompromised individuals should have a lower threshold for seeking care.

Understanding when home care is sufficient versus when professional medical attention is needed can be challenging. The vast majority of norovirus infections, while unpleasant, resolve on their own within a few days without any complications. However, certain warning signs indicate that the body may not be coping well and medical intervention could be beneficial or even lifesaving.

The most important factor to monitor is hydration status. Mild dehydration is expected during norovirus infection and can usually be corrected with oral fluids. However, moderate to severe dehydration is a medical emergency. Signs of significant dehydration include producing little or very dark urine, feeling dizzy or lightheaded especially when standing, having a rapid heartbeat, dry mouth and extreme thirst, and in severe cases, confusion or altered mental status.

Certain symptoms suggest something more serious than typical norovirus and warrant prompt medical evaluation. Bloody vomit or bloody or black tarry stools are concerning findings that require assessment. Severe, persistent abdominal pain beyond typical cramping should be evaluated, as should fever higher than 39°C (102.2°F). Symptoms that aren't improving after 3 days or that seem to be getting worse rather than better also merit medical attention.

Special considerations for vulnerable groups

Young children, particularly infants, should be evaluated by a healthcare provider earlier than adults because they can deteriorate quickly from dehydration. Parents should seek medical care if their infant or young child has had no wet diaper for 6 hours, is crying without tears, appears unusually drowsy or difficult to wake, has a sunken soft spot on the head, or is refusing to drink.

Elderly individuals and those with chronic health conditions should also have a lower threshold for seeking care. Pre-existing conditions like diabetes, heart disease, or kidney disease can be significantly worsened by the dehydration and electrolyte disturbances that accompany norovirus infection. Additionally, the symptoms of dehydration may be less obvious in older adults, making monitoring more challenging.

Pregnant women experiencing norovirus should stay in close contact with their healthcare provider. While norovirus itself doesn't directly harm the developing baby, severe dehydration during pregnancy can potentially cause complications. Pregnant women are also more susceptible to the effects of electrolyte imbalances. Adequate hydration is particularly important during pregnancy.

How Can You Prevent Norovirus Spread?

Prevent norovirus spread through thorough handwashing with soap and water for at least 20 seconds, disinfecting contaminated surfaces with chlorine bleach solution, washing contaminated laundry on the hottest setting, and avoiding food preparation for others until at least 48 hours after symptoms stop. Hand sanitizer is not as effective against norovirus as proper handwashing.

Preventing norovirus transmission is challenging given the virus's remarkable contagiousness and environmental stability, but consistent application of proven infection control measures can significantly reduce spread. The cornerstone of prevention is meticulous hand hygiene, as contaminated hands are a primary vehicle for transmitting the virus from person to person and from surfaces to mouth.

Handwashing must be done properly to be effective. Use warm running water and regular soap, lathering all surfaces of the hands including between fingers and under fingernails. Wash for at least 20 seconds, about the time it takes to sing "Happy Birthday" twice. Rinse thoroughly and dry with a clean towel or air dry. Critically, alcohol-based hand sanitizers are not as effective against norovirus as soap and water, so whenever possible, choose handwashing over sanitizer.

Environmental disinfection is equally important because norovirus can persist on surfaces for extended periods. Any surface that may have been contaminated with vomit or feces should be thoroughly cleaned and then disinfected with a chlorine bleach solution. The CDC recommends using a solution of 5-25 tablespoons of household bleach per gallon of water, depending on the surface. Allow the solution to remain on surfaces for at least 10 minutes before wiping.

Preventing spread in your household

When someone in your household has norovirus, taking immediate steps can help prevent other family members from becoming infected. If possible, designate a separate bathroom for the sick person's exclusive use. The infected individual should avoid preparing food for others and minimize contact with other household members until at least 48 hours after symptoms stop.

Contaminated laundry requires special handling. Wear rubber or disposable gloves when handling soiled clothing, towels, or bedding. Avoid shaking contaminated items, as this can disperse virus particles into the air. Wash items immediately using the hottest water setting appropriate for the fabric and dry on the highest heat setting. Wash your hands thoroughly after handling laundry.

High-touch surfaces should be disinfected frequently during an outbreak, including door handles, light switches, faucet handles, toilet handles, and countertops. Don't forget less obvious surfaces that are frequently touched, such as remote controls, phones, and computer keyboards. Regular disinfection throughout the illness and for several days afterward helps eliminate virus from the environment.

Preventing foodborne norovirus

Norovirus is the leading cause of foodborne illness outbreaks, so food safety practices are essential for prevention. People who are ill or recovering from gastroenteritis should not prepare food for others. Even after symptoms resolve, the CDC recommends avoiding food handling duties for at least 48 hours, and some guidelines suggest 72 hours for added safety.

Fresh produce should be washed thoroughly under running water before consumption, and fruits and vegetables that can be peeled should be peeled before eating. Be particularly cautious with shellfish, especially oysters, which can concentrate norovirus from contaminated waters. Cooking shellfish to an internal temperature of at least 63°C (145°F) for 15 seconds can reduce risk, though this may not eliminate all virus particles.

What Are the Possible Complications of Norovirus?

The main complication of norovirus is dehydration from fluid loss through vomiting and diarrhea. Severe dehydration can lead to electrolyte imbalances, kidney problems, and in extreme cases, cardiovascular complications. Young children, elderly adults, and immunocompromised individuals are at highest risk. Most healthy adults recover completely without complications.

While norovirus is usually self-limiting and resolves without lasting effects, complications can occur, particularly in vulnerable populations. Understanding these potential complications helps people recognize when home care may not be sufficient and medical intervention is needed.

Dehydration is by far the most common and important complication of norovirus infection. The combination of frequent vomiting and watery diarrhea causes rapid fluid loss that can outpace the body's ability to replace fluids through oral intake. Mild dehydration causes thirst, decreased urine output, and dry mouth. As dehydration worsens, symptoms progress to dizziness, rapid heartbeat, confusion, and eventually, if uncorrected, organ dysfunction.

Electrolyte imbalances accompany dehydration and can have significant effects on body function. Potassium, sodium, and other minerals are lost in vomit and diarrhea, and these imbalances can cause muscle weakness, irregular heart rhythms, and neurological symptoms. In severe cases, particularly in people with pre-existing heart or kidney conditions, these imbalances can be dangerous.

Complications in children

Children, especially infants and toddlers, are particularly susceptible to dehydration complications because of their smaller body size and higher metabolic rate. A child can become significantly dehydrated much faster than an adult with the same amount of fluid loss. Additionally, young children may be less able to communicate their symptoms or comply with oral rehydration efforts.

Severe dehydration in children can lead to reduced blood volume affecting organ function, particularly the kidneys. Signs of serious dehydration in children include extreme irritability or lethargy, sunken eyes, absence of tears when crying, and in infants, a noticeably sunken soft spot on the head. These findings require immediate medical attention and usually IV fluid resuscitation.

Long-term effects

For most people, norovirus causes no lasting health effects. However, some individuals, particularly those with inflammatory bowel disease or irritable bowel syndrome, may experience temporary worsening of their underlying condition following norovirus infection. Some people report temporary lactose intolerance after gastroenteritis, which usually resolves within a few weeks.

In immunocompromised individuals, chronic norovirus infection can occur, with symptoms persisting for weeks, months, or even years. This is most commonly seen in transplant recipients, people receiving chemotherapy, and those with primary immunodeficiency disorders. These individuals may require specialized medical management and careful monitoring.

How Is Norovirus Different from Food Poisoning?

Norovirus is actually a common cause of what people call "food poisoning." However, it differs from bacterial food poisoning in several ways: it has a longer incubation period (12-48 hours vs 2-6 hours for some bacterial causes), is primarily spread person-to-person rather than just through food, and doesn't respond to antibiotics since it's viral. Many cases of "24-hour flu" are actually norovirus.

The terms "food poisoning," "stomach flu," and "stomach bug" are often used interchangeably by the general public, but they represent different conditions with different causes. Understanding these distinctions helps in knowing what to expect and when to seek care. Norovirus is just one of many pathogens that can cause gastroenteritis, but it's the most common cause of acute gastroenteritis worldwide.

Bacterial food poisoning, caused by organisms like Salmonella, E. coli, or Campylobacter, typically results from consuming contaminated food products, particularly undercooked meat, poultry, eggs, or unpasteurized dairy. The incubation period varies by organism but is often shorter than norovirus for some toxin-producing bacteria. Bacterial infections may cause more severe symptoms in some cases and sometimes respond to antibiotic treatment.

Norovirus, while it can certainly be foodborne, also spreads readily through person-to-person contact and environmental contamination. This means you can get norovirus even if you haven't eaten anything suspicious. The person-to-person transmission is particularly important in explaining why norovirus causes large outbreaks in closed settings like cruise ships, schools, and nursing homes.

Key differences in symptoms and course

Norovirus typically causes more vomiting relative to diarrhea compared to some bacterial causes of gastroenteritis. The onset is characteristically sudden, with people often going from feeling fine to violently ill within hours. The illness typically resolves within 1-3 days, which is shorter than some bacterial infections that may persist for a week or longer.

Fever, when present with norovirus, is usually low-grade. High fever, bloody diarrhea, and severe abdominal pain are more suggestive of bacterial causes and warrant medical evaluation. These symptoms should prompt consideration of testing for bacterial pathogens and potentially antibiotic treatment if a bacterial cause is identified.

The post-illness contagious period also differs between viral and bacterial gastroenteritis. While norovirus shedding can continue for up to 2 weeks after symptoms resolve, some bacterial infections can result in a prolonged carrier state. This is particularly important for food handlers and healthcare workers who need clearance before returning to work.