Improved sample preparation has the potential to address a huge unmet need for fast turnaround sepsis tests that enable early administration of appropriate antimicrobial therapy. In recent years, inertial and elasto-inertial microfluidics-based sample preparation has gained substantial interest for bioparticle separation applications. However, for applications in blood stream infections the throughput and bacteria separation efficiency has thus far been limited. In this work, for the first time we report elasto-inertial microfluidics-based bacteria isolation from blood at throughputs and efficiencies unparalleled with current microfluidics-based state of the art. In the method, bacteria-spiked blood sample is prepositioned close to the outer wall of a spiral microchannel using a viscoelastic sheath buffer. The blood cells will remain fully focused throughout the length of the spiral channel while bacteria migrate to the inner wall for effective separation. Initially, microparticles were used to investigate particle focusing and the separation performance of the spiral device. A separation efficiency of 96% for the 1 µm particles was achieved, while 100% of 3 µm particles were recovered at the desired outlet at a throughput (sample + sheath) of 1 mL/min. Following, processing blood samples revealed a minimum of 1:2 dilution was necessary to keep the blood cells fully focus at the outer wall. In experiments involving bacteria spiked in diluted blood, viable E.coli were continuously separated at a total flow rate of 1 mL/min, with a separation efficiency between 82 to 90% depending on the blood dilution. Using a single spiral, it takes 40 minutes to process 1 mL of whole blood at a separation efficiency of 82% and 3 hr at 90% efficiency. To the best of our knowledge, this is the highest bacteria separation efficiency from blood sample reported using inertial and elasto-inertial methods. As such, the label-free, passive high efficiency and high throughput of bacteria isolation method has a great potential for speeding up downstream phenotypic and molecular analysis of bacteria.