Viral Pneumonia Pattern
Viruses predominantly cause interstitial pneumonia, characterized by bilateral interstitial infiltrates, though focal consolidation can also occur. 1
Radiographic Pattern of Primary Viral Pneumonia
The commonest chest radiographic abnormality in primary viral pneumonia is bilateral interstitial infiltrates, predominantly in the mid-zones, although focal consolidation is also well recognized. 1
Viral pneumonias are more commonly associated with interstitial syndrome and small subpleural consolidations on lung ultrasound, in contrast to bacterial pneumonia which shows larger consolidations and pleural effusion. 2
The interstitial pattern reflects the underlying pathophysiology: viruses cause primary damage to pulmonary capillary endothelium, leading to increased capillary permeability and interalveolar exudate with hyaline membrane formation. 3
Clinical Presentation Distinguishing Viral from Bacterial Patterns
Patients with primary viral pneumonia typically become breathless within the first 48 hours of fever onset, with an initially dry cough that may become productive of blood-stained sputum, accompanied by cyanosis, tachypnea, bilateral crepitations, and wheeze. 1
Primary viral pneumonia carries mortality rates exceeding 40% in hospitalized patients despite maximal intensive care support, with death typically occurring within 7 days of hospital admission due to rapid progression to respiratory failure. 1, 4
Contrast with Secondary Bacterial Pneumonia
Secondary bacterial pneumonia, which is up to 4 times more common than primary viral pneumonia, typically demonstrates a lobar pattern of consolidation on chest radiography, developing 4-5 days after initial symptom onset during early convalescence. 1, 4
Mixed viral-bacterial pneumonia shows lobar consolidation superimposed on bilateral diffuse lung infiltrates, carrying similarly high mortality rates exceeding 40%. 1, 4
Common Viral Pathogens and Their Patterns
Influenza A is the most common viral cause of hospital-acquired and healthcare-associated pneumonia in adults, while respiratory syncytial virus, parainfluenza, adenovirus, and influenza account for 70% of nosocomial viral pneumonia cases. 1
In community-acquired pneumonia requiring ICU admission, viral pathogens account for 22% of identified cases, with rhinovirus (8%), influenza (6%), metapneumovirus, RSV, parainfluenza, coronavirus, and adenovirus being the most common. 1
Clinical Pitfall: Misdiagnosis as Interstitial Lung Disease
Approximately half of patients undergoing bronchoalveolar lavage for suspected interstitial lung disease actually have viral pneumonia, with the most common misdiagnoses being acute fibrinous organizing pneumonia, cryptogenic organizing pneumonia, or chronic eosinophilic pneumonia. 5
The clinical characteristics and imaging findings of viral pneumonia overlap significantly with several interstitial lung diseases, making viral pneumonia frequently underrecognized in clinical practice. 5