Table 23.1.

ETIOLOGY AND INITIAL MANAGEMENT OF COMMUNITY-ACQUIRED PNEUMONIA^*

Patient Category	Common Organisms	Other Miscellaneous Organisms	Initial Therapy
Outpatient, no cardiopulmonary disease or other modifying risk factors	S. pneumoniae M. pneumoniae C. pneumoniae Respiratory viruses H. influenzae (in smokers)	Legionella M. tuberculosis Endemic fungi	Advanced-generation macrolide (e.g., azithromycin or clarithromycin) OR Doxycycline
Outpatient with cardiopulmonary disease and/or other modifying factors	S. pneumoniae M. pneumoniae H. influenzae Aerobic gram-negative bacilli Respiratory viruses Anaerobes C. pneumoniae	M. catarrhalis Legionella M. tuberculosis Endemic fungi	Oral quinolone (with activity against pneumococcus) OR β-Lactam plus macrolide
Hospitalized	S. pneumoniae H. influenzae Polymicrobial (including anaerobes) Aerobic gram-negative bacilli Legionella C. pneumoniae Respiratory viruses	M. pneumoniae M. catarrhalis M. tuberculosis Endemic fungi	Intravenous (IV) β-lactam plus IV or oral macrolide or doxycycline OR IV quinolone
Hospitalized, severe pneumonia	S. pneumoniae Legionella H. influenzae Aerobic gram-negative bacilli M. pneumoniae Respiratory viruses S. aureus	M. tuberculosis C. pneumoniae Endemic fungi	IV β-lactam plus either IV macrolide (azithromycin) or IV quinolone†

C. pneumoniae, Chlamydophila pneumoniae; H. influenzae, Haemophilus influenzae; M. catarrhalis, Moraxella catarrhalis; M. pneumoniae, Mycoplasma pneumoniae; M. tuberculosis, Mycobacterium tuberculosis; S. aureus, Staphylococcus aureus; S. pneumoniae, Streptococcus pneumoniae.

^*Excludes patients with human immunodeficiency virus infection.

^†If there is a high risk for Pseudomonas, adjust the regimen to include two antipseudomonal agents.

Modified from Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007;44(suppl 2):S27–S72.