Differences Between Influenza And Norovirus

Introduction

It is likely that you have experienced both influenza and norovirus at least once in your life, but what exactly makes them different? Influenza (often referred to as the flu) and norovirus (vomiting bug) are two distinct viruses that cause separate illnesses, each with its own set of symptoms, transmission routes, and treatments. In this article, we will explore the key differences between influenza and norovirus, including their causes, symptoms, duration of illness, complications, diagnosis, treatment options, and prevention strategies.

Causes and transmission

Influenza, or the flu, is caused by the influenza virus.¹ There are several types of influenza virus, including influenza A, B, C, and D. Influenza A and B are the most common in humans. These viruses can mutate over time through a process known as antigenic drift, which creates new strains that can cause seasonal outbreaks or pandemics.¹ 

Norovirus infection, or the vomiting bug, is caused by the highly contagious norovirus.² Norovirus is commonly found in the stool and vomit of infected individuals, and can survive on surfaces for an extended period of time. This means it is easily transmissible through contaminated food, water, or surfaces.² Norovirus can also spread from person to person through close contact or by inhaling airborne particles containing the virus.

Symptoms

Influenza and norovirus share some common symptoms, but there are also some key differences between the two to be aware of.

Influenza symptoms:

• Fever or feeling feverish/chills
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle or body aches
• Headaches
• Fatigue (tiredness)
• Occasionally, vomiting and diarrhoea, more common in children than adults^1,3

Norovirus symptoms:

• Nausea
• Vomiting
• Watery or loose diarrhoea
• Stomach cramps
• Low-grade fever
• Headache
• Muscle aches
• Generally feeling unwell²

Both influenza and norovirus can cause gastrointestinal symptoms like vomiting and diarrhoea, but these symptoms are more common and severe in norovirus infections because norovirus primarily affects the gastrointestinal tract. Influenza tends to cause more respiratory symptoms such as cough, sore throat, and congestion.

Incubation period

The incubation period refers to the time between when a person is exposed to the virus and when symptoms first appear. 

For influenza, the incubation period is typically around 1 to 4 days, with symptoms usually appearing within 2 days after exposure.⁴ The incubation period for norovirus is shorter, usually ranging from 12 to 48 hours.⁵ This means that people infected with norovirus may start experiencing symptoms relatively soon after coming into contact with the virus. 

Duration of illness

The duration of illness refers to how long symptoms typically last once they appear. 

Influenza symptoms often persist for about 7 to 10 days, although some individuals may feel unwell for longer periods, especially if complications develop.⁴ Norovirus illness tends to be shorter in duration, usually lasting from 1 to 3 days.⁵

Both influenza and norovirus can cause lingering symptoms or complications in certain cases, particularly in immunocompromised individuals (weakened immune systems) or underlying health conditions. 

Diagnosis

The diagnosis of influenza and norovirus infections is typically based on clinical evaluation and may involve laboratory testing in certain cases. 

Healthcare providers often diagnose influenza based on symptoms such as fever, cough, sore throat, body aches, and fatigue, particularly during flu season when influenza activity is widespread. Sometimes, they may perform rapid influenza diagnostic tests (RIDTs) or nucleic acid amplification tests (NAATs) to confirm the presence of the influenza virus in samples taken using respiratory swabs.⁴

The diagnosis of norovirus infection is primarily based on clinical symptoms, including nausea, vomiting, diarrhoea, and abdominal cramps, especially in the absence of other identifiable causes of gastroenteritis. Laboratory testing for norovirus is less commonly performed. Polymerase chain reaction (PCR) testing of stool samples can detect the presence of norovirus RNA.⁵

Healthcare providers may also consider the patient's medical history, recent travel, and potential exposure to individuals with similar symptoms when making a diagnosis of influenza or norovirus infection.

Treatment and management

The treatment and management of both influenza and norovirus infections is primarily through supportive care, which helps alleviate symptoms and prevent complications. 

For influenza, antiviral medications such as oseltamivir (Tamiflu), zanamivir (Relenza), and peramivir (Rapivab) may be prescribed, especially for high-risk individuals or those with severe illness.⁶ These medications work by inhibiting the replication of the influenza virus and can help reduce the duration and severity of symptoms if you start taking them early in the course of the illness.

If you have influenza, you should also get plenty of rest, stay hydrated, and take over-the-counter medications such as paracetamol or ibuprofen which can help reduce fever and relieve pain and discomfort. You should also take care to cover your coughs and sneezes, wash your hands frequently, and avoid close contact with others to help prevent the spreading of the virus. 

For norovirus infection, the main form of treatment is supportive care and making sure you are hydrated and have proper electrolyte balance, especially in cases of vomiting and diarrhoea that can cause you to become dehydrated.⁵ Taking oral rehydration solutions or even intravenous fluids may be necessary to replace the lost fluids and electrolytes. If you experience nausea and vomiting, you may also be prescribed antiemetic medications.

To prevent the spread of norovirus, you should take care to wash your hands frequently with soap and water, particularly after using the bathroom and before preparing or handling food. Contaminated surfaces and objects should also be cleaned and disinfected to reduce the risk of transmission to others.⁷

In both cases, you should avoid close contact with others, especially those who are at higher risk of complications, such as young children, the elderly, pregnant women, and immunocompromised individuals.^6,7 Take care to follow advice from your healthcare provider. 

Complications

Both influenza and norovirus infections can lead to complications, especially in vulnerable populations such as young children, the elderly, and the immunocompromised. However, many people are able to recover from either virus on their own at home. 

Influenza complications include pneumonia, bronchitis, sinus infections, ear infections, and worsening of underlying medical conditions such as asthma or congestive heart failure.⁸ These complications can result in hospitalisation and, in severe cases, may be life-threatening. 

Norovirus infections can also cause complications, although they are generally less severe than the ones that influenza can result in.⁹ Common complications of norovirus infection include dehydration due to vomiting and diarrhoea, particularly in young children and the elderly. Severe dehydration may require medical attention and intravenous fluids to prevent further complications.⁹ 

If you have symptoms of influenza or norovirus and you develop severe symptoms or signs of complications, such as difficulty breathing, persistent high fever, chest pain, or severe dehydration, you should seek medical care. Getting medical attention can help prevent any complications and help you receive appropriate treatment to support recovery from these viral infections.

Prevention

Vaccination is a key preventive measure for influenza, with annual flu vaccines recommended for individuals six months of age and older.¹⁰ These vaccines help stimulate the immune system to produce antibodies that provide protection against specific strains of influenza viruses circulating each year.

Vaccination not only reduces the risk of contracting influenza but also helps prevent severe illness, hospitalisation, and complications, especially among high-risk groups such as young children, older adults, pregnant women, and individuals with underlying health conditions.¹⁰

Practising good hygiene habits can help prevent the transmission of both influenza and norovirus. This includes frequent handwashing with soap and water for at least 20 seconds, especially after using the bathroom, before eating or preparing food, and after coughing, sneezing, or blowing your nose. If soap and water are not available, alcohol-based hand sanitizers can be used as an alternative. Try to avoid touching your face, particularly the eyes, nose, and mouth, to reduce the risk of transferring viruses from contaminated surfaces to mucous membranes.

During influenza season, individuals should also cover coughs and sneezes with a tissue or the inside of the elbow to prevent the spread of respiratory droplets containing the virus. Used tissues should be promptly disposed of in a trash bin, and hands should be washed afterwards to minimise the risk of contamination. 

If you are ill with influenza or norovirus, you should stay home from work, school, or social gatherings to prevent spreading the virus to others.

Summary

While influenza and norovirus share some similarities in their transmission routes and symptoms, they are caused by different viruses and have distinct characteristics that set them apart from each other. Influenza primarily affects the respiratory system and is known for causing seasonal outbreaks of respiratory illness, while norovirus is a cause of gastrointestinal illness worldwide.

Understanding the differences between influenza and norovirus is crucial for receiving appropriate treatment and practising effective prevention strategies. By implementing preventive measures such as vaccination, handwashing, and respiratory hygiene, individuals can reduce their risk of contracting influenza or norovirus and help protect vulnerable populations from illness and complications.