Infection of the lung tissue by a VIRUS. Causes of this type of pneumonia include ADENOVIRUSES, COXSACKIE VIRUSES, influenza virus or RESPIRATORY SYNCYTIAL VIRUS (RSV). Viral infections do not respond to ANTIBIOTICS and treatment is SYMPTOMATIC, with antibiotics used only if the patient develops secondary bacterial infection. In a previously healthy individual the viral infection usually gets better without treatment, but in vulnerable patients – the elderly or those with pre-existing disease – it can be fatal.