What is the difference between viral and bacterial infection on complete blood count?

Depends: As a generality bacterial infections elevate the total WBC and shift the differential count to the neutrophilic series. Viral infections often are not accompanied by large increases in the wbcs and the differential shifts to the right with lymphocytes and monocytes. Unfortunately, depending upon the specific infective agent, and the stage and severity of illness, this cannot be predicted.

See below: As a general rule bacterial infections produce an elevated WBC count with a preponderance of neutrophils and bands. Viral infections more often produce a low or normal WBC count with a preponderance of lymphocytes.