Introduction

Pneumonia is an infection of the air sacs within the lungs. It is mainly caused by viruses and bacteria and can affect one or both of your lungs. In this article, we will focus on viral pneumonia and the risk factors for developing these types of infections.

Viral pneumonia causes a range of symptoms in people.¹ In most cases, it causes a cough, fevers, chest pain, and some difficulty in breathing. The severity of the disease also varies – ranging from mild symptoms to hospitalisation in some cases. People admitted to the hospital often require oxygen to help with breathing as well as hydration through a drip. They also require further investigations such as chest X-rays, blood tests and throat/nose swabs.

There are certain risk factors which predispose people to viral pneumonia and more severe illness. Therefore, it is important that we understand these risk factors and how we can manage the risk. 

Common causes of viral pneumonia

Before we talk about the risk factors for viral pneumonia, it is important to get an overview of the most common types of viruses which cause pneumonia:^1,2

Influenza virus 

Otherwise known as ‘the flu’, influenza viruses can cause pneumonia and are particularly common during the wintertime. They often begin by causing generalised symptoms such as fever, headaches, muscle pains, and runny nose. However, they can then progress to cause symptoms of pneumonia. From here, further complications can arise, such as a bacterial lung infection, or infections elsewhere in the body.

Respiratory syncytial virus (RSV)

Respiratory syncytial virus is another very common type of virus which causes infections in all ages. Most generally, it causes the ‘common cold’ in adults or a condition called bronchiolitis in young children. However, it can also cause infections in the lungs leading to pneumonia. Outbreaks of this virus are common, particularly in hospitals and schools.

Coronaviruses (including SARS-CoV-2)

Coronaviruses are a family of a certain type of virus. Again, several of them are responsible for causing ‘common colds’. However, certain strains can cause more severe infections, including pneumonia. The COVID-19 pandemic was a clear example of this, where the rapid spread of SARS-CoV-2 caused a global pandemic and over 7 million deaths worldwide, many due to severe pneumonia.

Adenoviruses

Adenoviruses are another family of viruses which can cause the ‘common cold’. It tends to be slightly more common in children and can cause viral pneumonia.

Parainfluenza viruses

Parainfluenza viruses are a family of viruses which can cause viral pneumonia in children and adults. They are most commonly known for causing croup, a viral illness in toddlers which causes breathing difficulties.

Risk factors for developing viral pneumonia 

Age

Children younger than 5 and elderly patients (75+) are more susceptible to any type of infection. This is because a child’s immune system is still developing and an elderly patient's immune system does not work as well anymore. Additionally, elderly patients tend to have more underlying health problems, making them more susceptible to infections.¹

Pre-existing medical conditions

Some people have underlying health problems which directly affect their lungs. Conditions such as chronic obstructive pulmonary disorder (COPD) or asthma mean that the lung tissue doesn’t work as it normally should, making the patient less able to combat infections in the lung. These patient groups have a higher incidence of viral lung infections.³

Other conditions such as diabetes have more of an effect on your immune system. They are likely to dampen the immune response to infections in the body, resulting in more severe infections. 

Additionally, conditions affecting other organs can impede the body’s immune response to infection. Chronic conditions such as heart disease or chronic kidney disease will reduce the body’s reserve to combat infections. 

Weakened immune system

Evidently, the immune system is essential in combating infections such as viral pneumonia. There are some conditions which directly weaken the immune system and therefore reduce the power of the body’s immune response to infections. 

Poorly controlled HIV or AIDS can weaken the immune system. However, anti-HIV treatments in the UK are now widely available and very effective. This means that if someone regularly takes their medication, their immune system can function normally and the patient can live a very normal life. 

In some cancers, immunosuppressants or chemotherapy used to treat some cancers can weaken the immune system. This is because although these medications target cancer cells directly, sometimes they non-specifically kill other cells in the body, including immune cells. 

Lifestyle and environmental factors 

Other lifestyle and environmental factors can put you at increased risk of developing viral pneumonia: 

• Smoking: Smoking damages the lung tissues, making infections more likely to enter the lung
• Alcoholism: Alcohol weakens the immune system and impairs the body’s ability to fight infections
• Exposure to Air Pollution: Toxic gases in the air increases lung irritation and vulnerability to infections
• Crowded Living Conditions: Increases the chance of viral transmission when lots of people are in close proximity
• Occupational Hazards: Healthcare workers, first responders, and those working in high-risk environments (nursing homes, shelters) are more susceptible to infections due to increased exposure

Recent viral infections

People with recent viral infections are at greater risk of developing secondary pneumonia because of this. For instance, people with influenza or coronavirus infections sometimes develop secondary bacterial pneumonia. 

Hospitalisation and healthcare exposure 

Patients in healthcare facilities such as hospitals are at greater risk of exposure to hospital-acquired viruses. These are often different to the viruses commonly found in the general population. The proximity of unwell patients in hospitals also further enables the spread of viruses. 

Despite the increased risk of transmission of viruses in hospitals, the benefit of medical care for some patients still greatly outweighs the risk of hospital-acquired infection 

Special populations at higher risk 

There are a few groups of people who are specifically at risk for developing infections, including viral pneumonia. These are: 

Pregnant women

Pregnancy affects the body’s immune system. This is because the body is using more energy to provide for the growing baby, and there may be less reserve to combat infections.

Obese patients

Obesity causes higher rates of respiratory stress in the body. The lungs have to work harder when there is more fat tissue. This means that there are higher rates of complications of viral pneumonia in this population.

Malnourished patients

Malnourishment reduces the immune response in the body. This means these patients are less able to fight off infections. 

Prevention and management of risk 

Vaccinations 

Annual vaccinations are available for some viral infections. Examples of these are the yearly influenza and COVID-19 vaccinations for the high-risk groups. People in the high-risk category include the elderly, those with underlying health conditions, and healthcare workers. 

Vaccinations are highly effective against these respiratory viruses. A study showed the vaccine effectiveness for individuals who are fully vaccinated against COVID-19 was:⁴

• 97.2% vaccine effectiveness for the prevention of COVID-19-related hospitalisation 
• 99.0% vaccine effectiveness for the prevention of COVID-19-related death 

Management of chronic conditions 

As we have already established, chronic conditions such as diabetes, heart disease and chronic kidney disease put people at higher risk of infections, such as viral pneumonia. Close monitoring and medical management of these conditions reduce the risk of infections. 

Lifestyle modifications 

Modifying lifestyle factors like quitting smoking or reducing alcohol intake can reduce the risk of developing infections. 

Preventative healthcare 

Regular check-ups for high-risk individuals can aim to identify infections earlier in their course before they are clinically severe. This means treatment can be established earlier and reduce complications. Early treatment of viral infections can also reduce the risk of secondary bacterial infections. 

Summary

Viral pneumonia is a lung infection caused by viruses such as influenza, RSV, and coronaviruses, with varying severity from mild symptoms to hospitalisation. Risk factors include age (children and elderly), pre-existing medical conditions like COPD, asthma, and diabetes, a weakened immune system due to HIV, cancer treatments, and certain medications, as well as lifestyle factors such as smoking, alcoholism, and exposure to air pollution.

Individuals in crowded environments or healthcare settings, and those recently infected with another virus, are also at higher risk. Preventative measures include vaccinations, managing chronic conditions, lifestyle changes, and regular healthcare checks to reduce infection risk.