May be acquired from diverse environmental sources (i.e. tap water).
Bronchiectatics may be colonized (i.e. CF patients).
Must distinguish colonization from clinically significant infection.
Most common reason for isolation is colonization of the respiratory tract.
Most common true infections - blood stream infection (usually from vascular catheter) and pneumonia. Other manifestations rare (endocarditis, sinusitis, cellulitis, etc)
