Influenza And Respiratory Conditions

Introduction

Influenza is a respiratory infection caused by the influenza virus that targets and infects the nose, throat and lungs.¹ Influenza (flu) is contagious and the virus spreads predominantly by small droplets when an infected individual sneezes, coughs or talks.¹ Influenza virus infection is widespread with a billion cases of influenza infection every year all over the world.²

Influenza is usually a mild infection, with most patients recovering without treatment but in some individuals the patient is extremely sick and treatment is required.² These most at risk include:³

• Young children
• The elderly
• Pregnant women
• Immunocompromised individuals
• Individuals with cardiac disease
• Individuals with chronic lung disease

Respiratory condition is described as a disease that occurs in the lungs and respiratory system and can be caused by infection, air pollution or smoking. Influenza virus directly infects and replicates within the upper respiratory tract and causes inflammation of the upper respiratory tract, making influenza a respiratory condition. Influenza can cause severe sickness in three to five million cases every year and unfortunately is responsible for 290,000 - 650,000 respiratory deaths annually.² 

It is important to understand respiratory conditions to effectively manage and treat the condition, including prescribing the correct medication and providing patients with the correct support system to improve their lives. It is also important for prevention and control measures to reduce the number of patients from developing the condition and these measures can include vaccine programs, lifestyle changes and environmental intervention to reduce patients with respiratory conditions. It is crucial to understand influenza and the respiratory conditions it can cause and this article will be discussing the importance of understanding both influenza and respiratory conditions. 

Understanding influenza

There are four types of influenza virus:

1. Influenza A virus
2. Influenza B virus
3. Influenza C virus 
4. Influenza D virus 

Influenza A

Influenza A virus is responsible for the seasonal flu epidemics and is the more virulent type of influenza virus.² Influenza A virus is further classified into subtypes based on the combination of proteins expressed on the surface of the virus.² The proteins are Hemagglutinin (H) and Neuraminidase (N).³ There are 18 different H subtypes and 11 N subtypes³ but there have been more than 130 influenza type A combinations identified in nature⁴ but more can be found due to influenza's ability to reshuffle and rearrange its genes in a process called reassortment.⁴ The 2009 influenza pandemic was caused by influenza type A, subtype H1N1.²

Influenza B

Influenza B virus is also responsible for seasonal flu epidemics but it is milder when compared to influenza A virus.² Influenza B virus is not categorized into subtypes but is classified into lineages:²

• Type B/Yamagata
• Type B/Victoria

Both influenza B virus lineages circulate the world but the proportion of each influenza B lineage circulating can vary depending on geographical location and the season.⁴ However, influenza B/Yamagata virus is circulated less frequently compared to influenza B/Victoria which has circulated globally.⁴

Influenza C

Influenza C virus is a mild infection that is detected less frequently and as such, it is not of public health importance.²

Influenza D

Influenza D virus affects cattle and is not known to infect or cause illness in humans.²

Transmission of influenza

As discussed earlier, influenza is spread when an infected individual coughs, sneezes or talks and releases droplets that contain the virus, which then infects people in close contact.² Influenza can spread very quickly in crowded places such as schools, nursing homes and hospitals.² To prevent transmission, it is recommended for people to cover their mouths when they are coughing or sneezing with a tissue and to wash their hands regularly.

The severity, how long the epidemic will last, the age group affected, hospitalization rate and death vary significantly for each influenza season.³ In temperate climates, influenza infection peaks during the winter months whilst in tropical climates, Influenza virus is present all year.³ Everyone can become infected but there are specific groups that are at more risk compared to others as described earlier. Children under five, elderly, pregnant women, immunocompromised conditions such as HIV or cancer patients receiving chemotherapy, and patients with chronic health conditions such as chronic cardiac disease and lung condition are at higher risks of infections. Healthcare workers are also at 

Symptoms and clinical presentation

Influenza virus can vary from mild to severe infection and in some cases can lead to death.¹ Symptoms usually occur suddenly after infection and most patients experience some or all of the following symptoms:¹

• High fever,
• Cough and sore throat
• Runny or stuffy nose
• Headaches
• Fatigue
• Muscle and body aches
• Vomiting and diarrhoea (usually in children than adults)

Complications associated with influenza

Influenza can become a dangerous infection in some individuals and could become fatal. Influenza can cause the following complications:³

• Pneumonia: an infection in your lung caused by bacteria, viruses or lungs 
• Acute respiratory distress syndrome: a lung condition that causes low blood oxygen
• Myositis: is a disease where the muscles become inflamed and cause muscle fatigue
• Myocarditis: is the inflammation of the heart muscle, reducing the amount of blood pumped by the heart
• Multiorgan failure:  a severe, life-threatening condition where the organs fail to do their function, leading to urgent medical attention.

Diagnosis and management of influenza

Influenza is diagnosed clinically in a lab as it's difficult to differentiate from other respiratory illnesses using symptoms alone. Diagnostic methods include:

1. Rapid Antigen Tests: a lateral flow test that detects antigens such as nucleic acid detection.
2. Reverse transcription -Polymerase Chain Reaction (RT-PCR): is a method that detects genetic information of the virus. 

These diagnostic tools are preferred as they can give quick results within 15-30 minutes with high sensitivity and specificity and can also differentiate between the Influenza A virus and influenza B virus.³

Treatment options

Most influenza infection cases do not require any treatment as the immune system clears away the infection. However, for some individuals treatments are needed if the infection is severe. For mild symptoms, patients should stay and rest at home, making sure they are drinking plenty of fluids.² For patients with severe symptoms, they should seek medical care which includes antiviral medication and symptomatic relief.

Antiviral medications are a specific group of medicines that target viruses such as influenza virus and are used to clear away the virus and provide symptomatic relief. It is given to patients who are hospitalized due to the infection, individuals who have an existing health issue or immunocompromised individuals whose immune system cannot clear the infection. Antiviral medicines are important treatment options as they can fight off the infection, reduce how long the patient is sick and prevent transmission of the virus. 

Symptomatic relief is a medical therapy where the symptoms of the infection are treated and not the underlying cause (the influenza virus). This includes taking medicine like ibuprofen or Tylenol to treat fever, headaches and muscle aches which are associated with influenza infection. Taking a lot of rest and drinking water is important in providing symptomatic relief.²

Prevention strategies

The best way to prevent influenza is through annual vaccination² at the beginning of the winter season.³ A vaccine is effective at helping you avoid getting sick from the flu and can reduce the severity of the infection if you become infected, whilst also protecting high-risk patients from not transmitting the virus.

It is recommended for:²

• Children aged 6 months to 5 years old
• Pregnant mothers
• Individuals with existing medical conditions
• Elderly patients over 65 years. Vaccines become less effective in individuals over 65 years, so high dosages will be needed to provide protection³
• Health workers

Hygiene is another important strategy that can protect you from influenza. This includes washing and drying your hands regularly and avoiding touching your eyes, mouth and nose. As described earlier, covering your mouth and nose when coughing or sneezing prevents transmission of the infection which can prevent others from getting sick. It is also important to discard used tissues correctly and to wash your hands after doing so. 

Respiratory conditions associated with influenza

Pneumonia

Pneumonia is also a lung infection caused by bacteria, viruses or fungi. Influenza is associated with pneumonia due to several factors:

1. Primary viral pneumonia occurs when the influenza virus directly infects and targets the lower respiratory tract rather than the upper respiratory tract and this causes acute lung inflammation and alveolar damage and has a high mortality rate.⁵ 
2. Secondary bacterial pneumonia³ is caused when influenza suppresses the immune system, making it weaker whilst also simultaneously damaging the respiratory tract. This provides the perfect opportunity for another bacteria to infect and colonize the lungs, leading to a lung infection. 

Bronchitis

Bronchitis is a lung inflammation of the airways in the lungs caused by an infection. Influenza is associated with bronchitis³ as the virus can directly infect the bronchi tubes which leads to inflammation of the airways in the lungs. As discussed above, influenza weakens the immune system causing other microbes to infect the lungs more easily, causing bronchitis to occur. 

Acute respiratory distress syndrome (ARDS)

ARDS is a lung condition where fluid builds up in the alveoli (air sacs of the lungs), causing the lungs to struggle to fill up with air, leading to not enough oxygen in the blood and in the body. It can also cause scarring in the lungs and cause it to become stiff. ARDs are associated with influenza as the virus causes damage to the alveoli leading to ARDS to occur. 

Public health response to influenza outbreaks

Influenza poses a major public health problem and hence there must be measures to monitor the virus to manage and prevent an influenza pandemic. These can include:

1. Surveillance and monitoring:³ The World Health Organization monitors and conducts global surveillance of the virus to determine which strain is circulating in each geographical location and where the next pandemic could occur.
2. Knowing what strain of virus is circulating is important for vaccine development and distribution. Each vaccine has to be tailored against the virus type and subtype that is currently circulating to provide patients with the best protection. 
3. Communication strategies are another measure used to prepare the public for the flu pandemic. This can include influencing people to take their vaccine using the vaccine program, advocating for better hygiene and providing information for the public clearly and easily. 
4. An important public health response is for the healthcare system to be prepared for the wave of infection. As discussed earlier, influenza is very contagious and this means that many people will get infected in a short amount of time and this will create a burden on the healthcare system. Being prepared before the pandemic occurs is crucial in managing the influenza outbreak. 

Summary

Influenza virus is a contagious respiratory infection which is a public health problem. Influenza is a mild infection, with a majority of patients recovering without treatment but in some individuals, complications are making the patient extremely sick and treatment is required.² Treatments include antiviral medication, symptomatic relief and hospitalization. Influenza is associated with many respiratory conditions as the virus damages the lungs and surrounding airway and weakens the immune system, providing the perfect habitat for other microbes to inhabit and cause an infection. Prevention and management of influenza through vaccination programs and public health measures are key to preventing people from getting infected and developing further respiratory conditions.