Table 2.

Causative agents found in community-acquired pneumonia

Causative agents found in community-acquired pneumonia	In all patients U.S.A. (5)⁎	In patients presenting to EDs and primary care physicians with mild to moderate pneumonia (Fine Risk Class I–III) Canada (6)†	In patients requiring hospital admission U.S.A. (7)§
Viral	2–15%		12.7%
Bacterial
Unidentified		51.6%
Streptococcus pneumoniae	20–60%	5.9%	12.6%
Mycoplasma pneumoniae	1–6%	15%	32.5%
Chlamydia pneumoniae	4–6%	12%	8.9%
Haemophilus influenzae	3–10%	4.9%	6.6%
Staphylococcus aureus	3–5%	1.1%	3.4%
Moraxella catharralis	1–2%	1.1%	0.76%
Legionella spp.	2–8%		3.0%
Aspiration	6–10%
Enterobacteriaceae			2.8%
Pseudomonas spp.			1.7%
Pneumocystis spp.			1.4%
Mycobacterium tuberculosis			1.4%
Coxiella burnetii
Anaerobes
Mixed infection			2%

^⁎Based on integration of data from 15 studies on community-acquired pneumonia form North America.

^†Prospective randomized series enrolling 507 patients for the comparison of moxifloxacin and clarythromycin treatment.

^§Population-based active surveillance study of 2776 patients from Ohio.