Introduction

Viral pneumonia is a common respiratory disease caused by different infectious agents, including viruses. Typically, the causes of viral pneumonia include pathogens such as influenza viruses, RSV, and coronaviruses, among others. COVID-19 represents an introduced type of viral pneumonia caused by the SARS-CoV-2 virus with different clinical, diagnostic, and treatment aspects; hence, differentiation between viral pneumonia and the pneumonia of COVID-19 is critical to manage patients appropriately. This article surveys the fundamentally important differences between these two types of pneumonia, outlining pathophysiology, clinical presentation, imaging, diagnostics, and treatments according to recent peer-reviewed literature.

Pathophysiology

The pathophysiology of viral pneumonia is distinct from other forms of pneumonia and is driven by specific characteristics of viral infection.. Viruses such as influenza and RSV typically initiate infection in the upper respiratory tract and progress to the lower respiratory tract, where they cause inflammation and damage to the alveoli, disrupting oxygen exchange. This causes accumulation of Fluid in the lungs, leading to difficulty in breathing and hypoxemia. ¹

SARS-CoV-2, the virus responsible for COVID-19,  initiates infection through a distinct mechanism compared to other viruses.  It primarily binds to the ACE2 receptors, which are highly concentrated in the lungs. This causes a more intense inflammatory response, often triggering a"cytokine storm" which could result in lung damage. It is often much worse than similar viral pneumonia, with diffuse alveolar damage and microvascular thrombosis, which can lead to ARDS. ²  The main difference between COVID-19 pneumonia from the other forms of viral pneumonia is this hyperinflammatory response. ³

Clinical presentation

The typical presentation of viral pneumonia includes fever, cough, fatigue, and dyspnea. Symptoms are usually nonspecific and challenging to diagnose without laboratory tests =or imaging diagnostics. Myalgias and headaches can also occur with influenza-related viral pneumonia; wheezing is sometimes seen with RSV, especially in younger patients.⁴

COVID-19 pneumonia shares many of these clinical presentations. Additional features common to COVID-19 pneumonia include shortness of breath and hypoxemia. Other systemic symptoms, although less frequently reported, in patients with COVID-19 disease are anosmia (loss of smell), ageusia (loss of taste), and gastrointestinal upsets, which have been rarer in other viral pneumonia.⁵ Moreover, COVID-19 is often followed by thromboembolic complications, which are key indicators of the severity of the disease.⁶

An important clinical difference between COVID-19 and other viral pneumonias is the severity of progression.  The average incubation period of COVID-19 pneumonia is 8–12 days, with severe illness, where most of the patients end up being hospitalised for ARDS.⁷

Imaging findings

Imaging tests are one of the features that differentiate viral pneumonia from COVID-19 pneumonia. Viral pneumonia often appears inconsistent, with bilateral infiltrates in chest X-rays and ground-glass opacities (GGO) usually seen in the lower lobes.⁸ CT scans can further show more specific characteristics like the thickening of bronchial walls or nodular infiltrates, depending on the cause of the infection.

On the contrary, COVID-19 pneumonia usually has more diffuse ground-glass opacities and consolidations that are peripherally predominant and bilateral.⁹ A "crazy-paving" pattern on chest CT scans characterised by interstitial thickening with superimposed ground-glass opacities is characteristic of lung damage due to COVID-19.¹⁰ While viral pneumonia characteristically responds to treatment, radiological abnormalities in cases of COVID-19 may persist for months, signifying long-lasting lung injury and fibrosis.⁷

Laboratory diagnostics

Laboratory diagnosis of viral pneumonia shows elevated inflammatory markers such as C-reactive protein (CRP), leukocytosis, or lymphopenia; these findings are virus-specific but tend to present the same general patterns.⁸ Viral pathogens are typically identified by PCR or antigen tests, which confirm the presence of viral RNA or proteins.

Certain laboratory studies have been connected to COVID-19 pneumonia, including lymphopenia and elevated levels of CRP, D-dimer, and ferritin, all of which indicate an ongoing inflammatory process. Laboratory diagnosis of SARS-CoV-2 infection can be established through RT-PCR tests by detecting the presence of viral RNA in respiratory specimens. ¹¹ In severe cases, high concentrations of IL-6 and other cytokines have been identified as prognostic markers, which has led to the use of anti-inflammatory therapies to manage the symptoms.¹²

Other symptoms of COVID-19 patients include high levels of D-dimer and fibrinogen, which indicate a prothrombotic state, which are very unusual for other viral pneumonias.⁷ An increased propensity for a prothrombotic state is crucial in differentiating COVID-19 from other respiratory viral infections in laboratory testing.

Therapeutic approaches

The treatment of viral pneumonia would depend on the causative virus. Oseltamivir, an antiviral therapy, is considered effective in the case of influenza when used early in the infection period.¹³ The treatment consists mainly of supportive care, such as oxygen supplementation and mechanical ventilation in severe cases.

Given the novelty of COVID-19, treatment strategies have evolved over time. Antivirals like remdesivir provided improvement in the duration of hospital stay but failed to decrease mortality.¹⁴ However, corticosteroids, specifically dexamethasone, have become the cornerstones of severe COVID-19 pneumonia treatment by mitigating hyperinflammatory responses.¹⁵

Besides antivirals and corticosteroids, other monoclonal antibodies such as tocilizumab are currently used to neutralise the immune response in those patients who develop cytokine storms.16 Another treatment for COVID-19 pneumonia is using anticoagulants due to the potential threat of thromboembolic events, and it is less commonly associated with anticoagulation therapy when presented with other forms of viral infections.¹⁷

Prognosis and complications

The causative agent determines the prognosis of the viral pneumonia. For example, Influenza-associated pneumonia tends to carry a higher risk of death in elderly patients, especially those with comorbidities. Additionally, RSV-associated pneumonia may be particularly severe in infants or those with immunodeficiency.¹⁸

COVID-19 pneumonia has a different course than most other cases of viral pneumonia. While most patients present with mild to moderate illness, a subset of patients deteriorates significantly, often resulting in ARDS, multi-organ failure, and death. Older age, male sex, and underlying comorbidities, such as diabetes and hypertension, are significantly associated with severe outcomes in patients with COVID-19. Further complications with the long-term sequelae of post-COVID fibrosis, persistent fatigue, and cognitive dysfunction have been documented with severe pneumonia.¹⁹

Conclusion

Viral pneumonia has various similarities to COVID-19 pneumonia in clinical features, but it has crucial differences in its pathophysiology, radiological findings, laboratory diagnostics, and treatment strategies. The unique characteristics of COVID-19 pneumonia, such as hyperinflammatory response, prothrombotic state, and possible late complications, require specific therapeutic interventions; therefore, these two types of pneumonia should be differentiated for the effective management of patients in the time of the novel coronavirus pandemic. Continued research into the mechanisms and treatments of COVID-19 pneumonia will continue to give more insight into this new disease and help optimise outcomes in infected patients.

Frequently asked questions

What are the similarities and differences between viral pneumonia and COVID-19 pneumonia?

COVID-19 pneumonia can be caused by many viruses like influenza, RSV, and adenoviruses,; but COVID-19 pneumonia is caused by the SARS-CoV-2 virus. However, though both diseases affect the lungs and may be associated with respiratory symptoms, COVID-19 is much more aggressive and includes specific complications, such as cytokine storms and difficulties with clotting in the blood. ¹²

Could COVID-19 pneumonia be diagnosed with the same tests that diagnose viral pneumonia?

Both pneumonia types are commonly diagnosed through chest imaging modalities such as CT scans or X-rays to indicate lung inflammation and damage. Pneumonia caused by COVID-19 might show unique features, however. For example, ground-glass opacities on imaging have been reported. Additionally, a provisional diagnosis entails PCR tests and rapid antigen tests to establish the presence of SARS-CoV-2.⁸

Are the treatments for viral pneumonia and COVID-19 pneumonia the same?

Most of the treatment overlaps, including antiviral drugs and supportive care, with oxygen and ventilation. However, in the case of COVID-19 pneumonia, other medicines can also be used, such as corticosteroids like dexamethasone and anticoagulants to mitigate the inflammatory response and reduce the tendency to clot.¹⁵

What are some of the characteristics of COVID-19 pneumonia that make it especially dangerous compared to other types of viral pneumonia?

Another threat with COVID-19 pneumonia is that it more often leads to systemic complications, including the illness referred to as cytokine storm, ARDS, and also a higher risk of having blood clots that may lead to higher mortality rates, especially among those patients who have pre-existing conditions.¹⁷

Could vaccination help avoid both viral and COVID-19 pneumonia?

Most forms of viral pneumonia, for instance, those caused by influenza and by SARS-CoV-2, are preventable by vaccines. To say the least, the COVID-19 vaccines have already been proven to prevent more severe cases and have a very low hospitalisation rate. In contrast, the flu vaccines reduce the risk of severe influenza-related pneumonia.