Peripheral Blood Eosinophilia in Patients with Diabetic Foot Infection Receiving Long-Term Antibiotic Therapy

Background: The eosinophil level in peripheral blood increases in response to various conditions, the most common being medication use. Since the outcome of increased levels of eosinophils can range from a benign finding to extensive damage to host organs and systemic consequences, this finding raises concern among clinicians. We aimed to assess the prevalence of prolonged antibiotic-therapy-induced eosinophilia and possible outcomes. Methods: We conducted a retrospective cohort study of diabetic patients admitted to the orthopedic department from December 2016 through December 2020 due to a moderate to severe diabetic foot infection and who received at least 14 days of antibiotic therapy. Patients were identified retrospectively through the orthopedic department registry, and their files were reviewed, extracting demographics, laboratory test results, antibiotic treatment, and outcomes. Results: The cohort included 347 patients; a total of 114 (32.8%) developed eosinophilia during the follow-up period. Patients who developed eosinophilia had a significantly longer duration of antibiotic treatment (p < 0.001) and a significantly longer hospitalization (p = 0.001). For multivariable analysis, the independent risk factors predicting drug-induced eosinophilia included older age, higher eosinophil count on admission (per quantile) and higher platelet count on admission (per quantile) (p = 0.012, p < 0.001, p = 0.009, respectively). There was no evidence of complications in patients who developed eosinophilia compared to patients who did not. No significant association with a specific type of antibiotic was found. Conclusions: We found a higher incidence of drug-induced eosinophilia than expected or previously described. The factors associated with eosinophilia included age and higher baseline eosinophil and platelet levels but not antibiotic type.