The most common causes of community-acquired pneumonia are viral infections Beyond the neonatal period, the most common bacterial cause is pneumococcus Less common, but more severe bacterial causes of pneumonia include S aureus and GAS While chest radiography can be useful to evaluate for complications of pneumonia, such as empyema or lung abscess, radiographic appearance alone is not useful for differentiating viral from bacterial etiologies Current Evidence The most common causes of pneumonia in different age groups are listed in Table 94.13 The most common causes are viral Among the bacteria, S pneumoniae predominates at every age beyond the newborn period S aureus causes a severe, rapidly progressive but uncommon pneumonia in young children; 60% of these infections occur in the first year of life GAS is also uncommon but may also be severe Anaerobic bacteria play a role primarily following aspiration TABLE 94.13 MOST COMMON CAUSES OF PNEUMONIA BY AGE Age Viral Pyogenic bacteria Other