Table 1. Comparison of respiratory exacerbations with acute bacterial infections.

	Acute bacterial respiratory infections	Respiratory exacerbations
Bacterial density (compared to baseline)	High	Normal
Bacterial community diversity (compared to baseline)	Low	Normal
Culture growth	Usually	Occasionally
Airway inflammation	High Proportionate to microbial burden	High Disproportionate to microbial burden
Sepsis	Common	Never/rare
Clinical benefit of antibiotics	Rapid, unambiguous	Inconsistent, subtle
Relevance of in vitro susceptibility	Critical to clinical response	No relation with clinical response