A method and microfluidic device useful for isolating microbes from a blood sample which includes introducing the blood sample into the sample inlet of a spiral microfluidic device; and introducing a second fluid into the sheath inlet of the microfluidic device, wherein the spiral channel terminates in a microbe outlet and a waste outlet, and wherein the spiral channel includes a length, height, and a width that define an aspect ratio adapted to isolate any microbes present in the sample along a first portion of the spiral channel terminating at the microbe outlet, and to isolate red blood cells and leukocytes along a second portion of the spiral channel terminating at the waste outlet; and collecting the microbes from the microbe outlet, thereby isolating the microbes.