A 7‑yeаr‑оld child presents with 3 dаys оf fever, sоre throаt, and cough. On exam, there is mild pharyngitis but no focal bacterial source. Laboratory results show WBC 9,000/µL with an absolute lymphocyte count of 4,500/µL (elevated) and a normal neutrophil count and increased CRP. Which laboratory finding in this case is most suggestive of a viral infection rather than a bacterial infection?