Community-Acquired Pneumonia Diagnosis and Differentiation

Primary Differentiation: Setting of Acquisition

Community-acquired pneumonia (CAP) is defined as pneumonia occurring in patients without recent hospitalization, residence in a nursing home, or recent intravenous antibiotic therapy, chemotherapy, or wound care, according to the American Journal of Respiratory and Critical Care Medicine 3
The setting of acquisition is the primary distinction between CAP and other forms of pneumonia, as clinical features cannot reliably differentiate between them, as stated by Clinical Infectious Diseases and Thorax 1, 2

Clinical symptoms such as fever, cough, sputum production, pleuritic chest pain, and abnormal breath sounds cannot reliably distinguish CAP from other pneumonia types, as noted by Clinical Infectious Diseases and American Journal of Respiratory and Critical Care Medicine 1, 3
The American Thoracic Society states that clinical characteristics cannot establish etiologic diagnosis with adequate sensitivity and specificity, although this information is also available from Praxis Medical Insights, the American Thoracic Society guideline is preferred 4
A chest radiograph (PA and lateral) showing new infiltrate is required to establish pneumonia diagnosis and differentiate from acute bronchitis, as recommended by Clinical Infectious Diseases, Thorax, and other sources 1, 2, 6

The British Thoracic Society explicitly states that the terminology of "typical" versus "atypical" pneumonia has outgrown its historical usefulness and should not be used, as also noted by Praxis Medical Insights, however the British Thoracic Society guideline is preferred 2, 5
Empiric therapy for CAP should cover both typical and atypical pathogens regardless of presentation, as recommended by the American Journal of Respiratory and Critical Care Medicine and other sources, although Praxis Medical Insights also provides this information 3, 4, 5
Do not delay antibiotics while attempting etiologic diagnosis, as mortality increases when first antibiotic dose is delayed, as noted by American Journal of Respiratory and Critical Care Medicine 3