Introduction

Differentiating between viral pneumonia and influenza can sometimes be challenging. Viral pneumonia is the infection of the lungs by a virus that causes irregularities in the exchange of carbon dioxide and oxygen in the alveoli, leading to inflammation.¹ On the other hand, influenza is a contagious viral disease that is easily transmissible and predominantly affects the lower and upper respiratory tracts.² By acknowledging the main differences between viral pneumonia and influenza, the treatment and diagnosis process can be improved. In this article, we will discuss the causes, mode of transmission, symptoms, diagnosis, risk factors, and treatment approaches that will provide a full guide towards distinguishing between the two conditions. 

Causes

The main and most common causes of viral pneumonia are:¹

• SARS-CoV-2 (coronavirus)
• Respiratory syncytial virus (RSV)
• Influenza A, B, and C virus
• Human metapneumovirus 
• Adenovirus 
• Varicella-zoster virus
• Herpes simplex virus
• Minimi virus cytomegalovirus (CMV)
• Measles

Whereas, the main causes of influenza specifically include Influenza A and B.³

Mode of transmission

Viral pneumonia and influenza have similar modes of transmission as viral pneumonia is mainly transmitted by coughing and sneezing as it leads to respiratory droplets in the air, which can be inhaled by another individual who is in close contact with the infected individual and contaminated surfaces.⁴ Influenza predominantly spreads through the inhalation of infectious respiratory droplets produced by the infected individual via speaking, coughing, and sneezing.⁵

Comparison of symptoms

Viral pneumonia presents with common symptoms of respiratory tract infection, which include the following: 6

• Coughing (with mucus)
• Shortness of breath
• Fever
• Chest pain (higher predominance than in influenza due to lung inflammation)
• Wheezing
• Fatigue

Influenza symptoms include:²

•  Sore throat
• Dry cough
• High fever (higher predominance than in pneumonia)
• Runny nose
• Fatigue
• Muscle aches
• Headache

Onset and duration of symptoms

Pneumonia has a gradual onset of action because it develops at a slower pace than other respiratory infections and might take a few days to become detectable. It can start as a normal cold and flu and gradually progress into pneumonia; this action might take three to five days. For cases which are considered to be moderate, their symptoms will last around one to two weeks, but for severe cases, it may take months.^1,6 

Influenza has a sudden onset of action compared to pneumonia. It can take one to four days for the symptoms to be noticeable and can persist for seven to ten days. Groups who are at high risk are those with cardiac disease, chronic lung diseases, and pregnancy because pneumonia can develop 48 hours after the start of the symptoms.² 

Physical exam and diagnostic differences

Physical examination for viral pneumonia includes lung sound assessment to detect any crackles or wheezing because of inflammation and fluid. Some areas of the lung will have lower breathing sounds due to the lung’s solidification, known as consolidation. In patients with influenza, the lung will usually sound normal unless there are complications.

Tachypnea, dyspnoea, and tachycardia are much more frequent in viral pneumonia than influenza. Chest X-rays will detect any consolidation or fluid (pus) found in either lung in patients with viral pneumonia. Whereas in patients with influenza, a chest X-ray will usually come out normal.

Polymerase chain reaction (PCR), which is a highly sensitive test, can be used for both influenza and viral pneumonia to detect coronavirus, RSV, and influenza A or B. Rapid influenza diagnostic (RIDT) is used to detect influenza antigens, but it's less sensitive.^7,8

Risk factors

Risk factors associated with viral pneumonia 

There are many risk factors associated with viral pneumonia, which includes:^1,2

• Age
  • Young children and infants are at risk of viral pneumonia because their immune system is still developing
  • As we grow old, the immune system weakens, which makes the elderly aged 65 and above highly susceptible to pneumonia
• Prior health conditions
  • People with chronic obstructive pulmonary disease (COPD) and asthma are likely to develop viral pneumonia  
  • Heart conditions and heart failure tremendously weaken the immune system, therefore increasing the chance of developing viral pneumonia
• Smoking
  • Smoking destroys the lungs and increases the production of mucus and pus

Risks associated with influenza 

Influenza has a severe effect on:^1,2 

• Young children
• Pregnant people
• Elderly people
• People with health problems which are considered to be chronic  

Treatment approaches

The key treatments for viral pneumonia includes:¹

• Prioritisation of supportive care, which includes maintaining oxygenation as much as needed - this could be given through nasal cannula
• Maintaining hydration either by supervised intravenous fluids or oral intake
• Resting
• Antiviral therapies can be used for viral pneumonia as well as prophylactic or preventive therapies for individuals who are at a higher risk

Supportive care for patients with influenza includes:⁹ 

• Rest
• Over-the-counter medication for pain and fever
• Hydration
• Antiviral medication can also be taken, such as oseltamivir

Complications

Complications associated with viral pneumonia are acute respiratory failure, bacterial infection leading to abscess, sepsis which can lead to organ failure, cardiovascular complications, and acute respiratory distress syndrome.¹

Complications of influenza are that it can cause both viral and bacterial pneumonia, ear and sinus infections, inflammation, and the worsening of chronic conditions such as asthma and congestive heart failure.²    

Prevention

The following can be done to prevent viral pneumonia:¹⁰

• Keeping up to date with vaccinations, including vaccinations against coronavirus (COVID-19) and influenza
• Maintaining good hygiene
• Eating healthy
• Giving up smoking
• Exercising regularly

For influenza, it's highly recommended to:^11,12

• Vaccinate at the start of flu season (typically at the start of autumn in October) 
• Protect yourselves from the transmission of influenza with face masks
• Maintain good hygiene
• Avoid close contact with infected individuals          

Summary

Nevertheless, viral pneumonia and influenza are predominantly linked to respiratory infections, which have an overlap in some symptoms. The symptoms include coughing, fatigue, and fever. The differences between both infections have to do with the onset of action, severity, and the process of progression. 

Viral pneumonia tends to have a slower onset compared to influenza. On the other hand, influenza typically manifests with a much quicker sudden onset, leading to symptoms such as a dry cough, muscle aches, and a higher prevalence of fever. Diagnostic tests and physical examinations play a huge role in differentiating between viral pneumonia and influenza. Viral pneumonia will cause crackles and wheezing under the stethoscope. A chest X-ray will demonstrate consolidation of one or both lungs. On the other hand, individuals with influenza will have a normal lung sound and a clear X-ray unless there are secondary infections.

Properly diagnosing the patient can significantly assist in the treatment options for both conditions. Recognising the differences between the two infections can significantly reduce the risks and improve the recovery process.