Viral pneumonias are rare in comparison to bacterial pneumonias, accounting for about 5% of pneumonias in the UK.
- the respiratory syncytial virus is the most common agent. It may be indistinguishable from acute bacterial bronchitis or bronchiolitis and is often accompanied by a skin rash. It is unresponsive to antibiotics.
- adenovirus may produce viral pneumonia in children and young adults. It more commonly causes upper respiratory tract disease with prominent rhinitis but on occasion, may produce lower respiratory tract disease, including bronchiolitis and pneumonia.
- the principle viral cause of pneumonia is influenza A virus. This usually occurs during epidemics of influenza A - Asian 'flu - but is very rare. The condition develops rapidly with progressive dyspnoea; acute haemorrhagic disease of the lungs may cause death within hours. However, the most common cause of pneumonia during influenza epidemics is secondary bacterial infection, usually with Staphylococcus aureus or Streptococcus pneumoniae.
Other viruses which may affect the lung directly include those of measles, chickenpox and herpes zoster.
Diagnosis is confirmed by a rise in specific antibody titre.