Viral Pneumonias

Viral pneumonia is prevalent among both immunocompetent and immunocompromised hosts, typically causing more severe disease in the latter. Several viral pneumonias, such as influenza, HMPV, RSV, and parainfluenza demonstrate similar airway-centric distribution, the likelihood of a specific organism often dependent on seasonal epidemics. Other viral pneumonias, such as adenovirus, frequently cause pneumonias with imaging findings indistinguishable from community-acquired bacterial pneumonias. For a few organisms, additional factors are central to the likelihood of infection, for example, environmental exposure for Hantaviruses and vaccination status for Varicella. In organisms that typically cause chronic infections in humans, such as HSV and CMV, the relationship between infection and clinical pneumonia is complex and incompletely understood.