- Pneumonia is a generic term referring to bacterial, fungal, or viral infection of the lung. Pneumonias can be categorized in multiple ways which either highlight the infectious etiology, patient population, the clinical setting of infection, the appearance on chest radiography, or the pattern of symptomology. Clinicians typically categorize pneumonias based on their clinical setting of transmission as this helps narrow down the possible list of agents for purposes of antibiotic selection. Consequently, the two most fundamental categorizations of pneumonias are those whose transmission occurs in the general community, termed community-acquired pneumonias, and those whose transmission occurs in the Hospital setting, termed hospital-associated pneumonias. A few specialized organisms can cause disease but almost exclusively in immunocompromised patients.
- Infection of the lung parenchyma ultimately requires inoculation of the lower respiratory tract with causative agents as well as a failure of normal Pulmonary Immunity (see page). Pathogens can access alveoli either through inhalation of contaminated respiratory droplets, small-scale aspiration of oropharyngeal contents, and rarely through direct hematogenous spread or direct invasion from an extra-pulmonary location.