This is a simple algorithm for bloodstream infections associated with PICC lines, etc. taken from a reviewer for the Critical Care Medicine board examination. [see reference below].
Clues to a central line infection: compare time to growth of culture taken from central line vs. peripheral IV, and compare CFUs from the two cultures. Less time to growth and higher CFU counts from central line suggests that source of infection may be the central line.
Parillo, Joseph, Edward Viner, and Henry Masur. Adult Multiprofessional Critical Care Review Course. 2010. Print.