Community-acquired pneumonia is caused by a defined set of microbial pathogens—predominantly bacteria (notably Streptococcus pneumoniae as a pyogenic organism, and atypical organisms such as Mycoplasma, Chlamydophila, and Legionella) alongside a minority of viral causes—and empirical antibiotic therapy is selected to cover the most likely pathogens before culture results are available, since diagnostic testing is reserved for higher-severity cases and antiviral treatment is generally not applicable except for influenza. Severity stratification determines both the intensity of diagnostic microbial testing and the breadth of empirical antibiotic coverage required, reflecting the principle that treatment must balance pathogen coverage against the clinical risk of undertreatment.
Community-acquired pneumonia is caused by a defined set of microbial pathogens—predominantly bacteria (notably Streptococcus pneumoniae as a pyogenic organism, and atypical organisms such as Mycoplas…