Changes in eosinophil count during bacterial infection: revisiting an old marker to assess the efficacy of antimicrobial therapy

Introduction: Eosinopenia as a criterion of sepsis has been the subject of debate for decades. Different authors have proposed different cut-off values.

Methods: A prospective study was conducted from February to August 2016. Hospitalized adults suffering from a bacterial infection with eosinopenia, defined as an eosinophil count <100/mm³, were included. Patients were divided into two groups according to the first day of effective antimicrobial therapy. They were observed for 5days in order to evaluate whether recovery from eosinopenia was predictive of an appropriate antibiotic regimen.

Results: One hundred and twenty-two patients were screened and 96 were included. Group 1 patients (n=70) received effective antimicrobial therapy from day 0. Their eosinophil count increased significantly between day 0 and day 1 (p<0.0001). Group 2 patients (n=26) received delayed effective antimicrobial therapy, and there was no significant difference in eosinophil count between day 0 and day 1 (p=0.55). Moreover, eosinophil counts normalized on day 5 in both groups. The mean duration of antimicrobial therapy was comparable in the two groups (7.7±1.16 days). The antibiotics most often prescribed in both groups were intravenous cephalosporins. During follow-up, all patients were considered to be cured after day 30.

Conclusions: The eosinophil count appears to normalize faster than C-reactive protein (CRP) and polymorphonuclear neutrophils in eosinopenic patients on appropriate antimicrobial therapy. This simple test is easy to perform as part of a regular complete blood count, with no additional costs as required for CRP or procalcitonin.