Introduction 

Norovirus, commonly referred to as the stomach bug, is one of the main causes of acute gastroenteritis, an inflammation of the stomach and intestines. Norovirus is a highly contagious viral infection that most commonly presents with symptoms such as vomiting, nausea, stomach pain, and dehydration. Although symptoms typically resolve within 3 days, severe or long-term consequences can persist and may require hospitalisation. Severe complications are usually seen in young children, the elderly, or immunocompromised people.^1,2

Norovirus outbreaks occur worldwide across all age groups, with lower-income countries experiencing a greater disease burden. Approximately 685 million cases of gastroenteritis are reported annually, a large proportion of which is attributed to norovirus infection. In addition, new variants of the virus are emerging, making vaccination challenging and leading to greater hospitalisation and mortality rates in those affected. Norovirus infection is transmitted through the faecal-oral route, which involves contaminated food, water, and surfaces, as well as person-to-person transmission. This article will explore norovirus and the severe complications associated with the infection.^1,2,3

What is norovirus?

Norovirus is a highly contagious viral infection that leads to acute gastroenteritis, particularly in children. Studies suggest that the virus infects and replicates within immune cells lining the gastrointestinal tract, particularly the epithelial cells of the intestine(quote the study). This can disrupt gut functions and contribute to the observed symptoms associated with infection, including vomiting and diarrhea. Norovirus is also extremely infectious, with just a few viral particles enough to trigger an infection. On average, the time from exposure to the virus to the production of symptoms is about 1.2 days, with symptoms typically lasting between 1 to 3 days. However, the virus can be shed in stool for up to 60 days, and even longer in individuals with weaker immune systems.¹

The appearance of different strains or variants contributes to worldwide outbreaks. Noroviruses are categorised into multiple genogroups, with genogroups I, II, and IV primarily responsible for human infections. Of those, variants and strains within the genogroups contribute to transmissibility and outbreaks. Studies suggest that person-to-person transmission is most common. Gastroenteritis outbreaks can occur in different settings, such as hospitals, schools, and cruise ships. The incidence is often higher during the winter months. Contaminated food, water, and surfaces are also potential modes of transmission.^1,3,4

Detection of a norovirus outbreak typically involves reverse transcription polymerase chain reaction (RT-PCR) or enzyme immunoassays, which are methods to detect the virus through stool or emesis samples in the lab. In addition to laboratory tests, the Kaplan clinical criteria are also widely used to detect the probability of an outbreak:^1,2

• Vomiting occurs in more than half of cases
• The average incubation period, or the time it takes to develop symptoms after exposure, is 24 to 48 hours
• Average length of symptoms of 12-60 hours 
• No bacterial cause detected in laboratory tests

Common symptoms of norovirus infection

Symptoms of norovirus infection most commonly include:¹

• Nausea 
• Vomiting 
• Dehydration
• Stomach pain 
• Diarrhea
• Cramping
• Muscle pain
• Headache 

Although most people recover within 1-3 days without complications, some people, especially those with underlying conditions, may experience severe complications.¹

Severe complications of norovirus infection

Severe dehydration

One of the most common and dangerous complications of a norovirus infection is dehydration due to persistent vomiting and diarrhea. This can lead to electrolyte imbalances, including hypokalemia (low potassium levels) and hyponatremia (low sodium levels), impaired kidney function, and even death in some cases. Detecting dehydration and immediate treatment are essential. Signs of dehydration include tiredness, dry throat and mouth, low urine output, dizziness, and tachycardia (rapid heart rate). Oral rehydration therapy is generally recommended, which includes plenty of electrolytes. However, severe dehydration or persistent vomiting may necessitate hospitalisation and intravenous hydration.^1,2,3

Neonatal necrotizing enterocolitis

Several studies have identified a connection between norovirus infection and necrotizing enterocolitis in infants. This condition involves inflammation of the intestine, which leads to bacterial invasion and intestinal tissue death. The condition can be deadly and usually requires surgery. A study investigating the cause of a necrotizing enterocolitis outbreak in a neonatal intensive care unit found norovirus-like particles in samples of all those infected. Additionally, those infected were typically younger, had lower overall health scores, and had received antibiotics, which highlights the importance of age and immune status in susceptibility to severe complications. The study also found that proximity to each other, as well as a healthcare worker with gastroenteritis, also played a role in the outbreak, emphasising the contagious nature of norovirus infections.^1,5,6 

Benign convulsions (seizures) associated with mild gastroenteritis

In children, norovirus infection can be associated with benign convulsions (or seizures), often occurring alongside mild gastroenteritis. These cases have also been increasing annually. Although the exact mechanism by which the viral infection is linked to neurological effects is not fully understood, the seizures are usually brief and resolve on their own, with the condition typically having good overall outcomes.^3,7,8

Hemolytic uremic syndrome

Recent studies have found norovirus to be associated with hemolytic uremic syndrome, where the virus causes damage to blood vessels in the kidneys, leading to red blood cell damage, low platelet levels, and acute kidney injury. As of 2022, five cases of norovirus-associated hemolytic uremic syndrome have been reported, four of which had underlying conditions. This suggests that pre-existing health issues can lead to greater severity of complications in norovirus infections.^9,10

Risk factors for severe complications

Some factors could increase the risk of either contracting or experiencing severe complications from norovirus infection, some of which include:^1,2,3,6 

• Age: The elderly and young children are especially susceptible to severe complications following infection 
• Immune status: People with compromised immune systems, such as cancer patients or those who have undergone an organ transplant, are more at risk
• Underlying conditions: People with pre-existing conditions, such as kidney disease, can increase the severity of infection and lead to more complications 
• Proximity to infected people: Living in or visiting crowded environments can promote the virus 
• Food handlers: While preparing or producing food, contamination can occur. High risk of contamination is seen in food served raw, such as fruits and vegetables 

Prevention and management 

Prevention

Several recommendations have been provided to prevent norovirus outbreaks. Some of these include: ¹

• Hand hygiene: Wash your hands with soap and running water for more than 20 seconds. Alcohol sanitizers may be used, but they are less effective than frequent handwashing
• Clean surfaces: Clean surfaces, including sinks, tables, and toilets, with bleach
• Food safety: Wash fruits and vegetables and cook seafood thoroughly 
• Contact: Avoid contact with infected individuals for at least 48 hours after their symptoms have stopped

Management

Managing norovirus infection involves targeting symptoms. Methods to reduce the risk of a norovirus outbreak are also essential. ¹

• Oral rehydration therapy: This form of therapy is used for dehydration, which is commonly caused by diarrhea. It includes plenty of electrolytes, glucose, and water. In severe cases or if vomiting is severe, intravenous hydration is used
• Symptom relief: Over-the-counter medications can be considered for nausea and vomiting 
• Frequent monitoring: Closely monitoring young children, the elderly immunocompromised individuals and those with underlying conditions is essential as they are more likely to experience severe symptoms 

Summary 

Norovirus, or the stomach bug, is a highly contagious viral infection affecting people of all ages. As one of the leading causes of acute gastroenteritis, it commonly presents with symptoms including vomiting, nausea, stomach pain, and dehydration. Although these symptoms typically resolve within 3 days, some people experience severe complications that can even lead to death. Young children, the elderly, immunocompromised people, and those with underlying disease are most susceptible to severe complications. Some of the severe complications include severe dehydration, neonatal necrotizing enterocolitis, benign convulsions associated with mild gastroenteritis, and hemolytic uremic syndrome. The contagious nature of the disease highlights the importance of monitoring and avoiding close proximity with infected people, especially in high-risk groups. The most important preventative method for norovirus infection is frequent handwashing with soap and running water, as well as bleaching surfaces regularly. Managing infections typically involves oral rehydration therapy, while intravenous fluids may be used in severe cases. Recognising and acting promptly are critical to reducing complications and mortality associated with them.