Patient predictors of pathogenic versus commensal Gram-positive bacilli organisms isolated from blood cultures

Objective: Gram-positive bacilli represent a diverse species of bacteria that range from commensal flora to pathogens implicated in severe and life-threatening infection. Following the isolation of Gram-positive bacilli from blood cultures, the time to species identification may take upward of 24 hours, leaving clinicians to conjecture whether they may represent a contaminant (inadvertent inoculation of commensal flora) or pathogenic organism. In this study, we sought to identify patient variables that could help predict the isolation of contaminant versus pathogenic Gram-positive bacilli from blood cultures. Design: Retrospective cohort study. Settings: One quaternary academic medical center affiliated with the University of Toronto. Patients: Adult inpatients were admitted to hospital over a 5-year period (May 2014 to December 2019). Methods: A total of 260 unique Gram-positive bacilli blood culture results from adult inpatients were reviewed and analyzed in both a univariable and multivariable model. Results: Malignancy (aOR 2.78, 95% CI 1.33-5.91, p = 0.007), point increments in the Quick Sepsis Related Organ Failure Assessment score for sepsis (aOR 2.25, 95% CI 1.50-3.47, p < 0.001), peptic ulcer disease (aOR 5.63, 95% CI 1.43-21.0, p = 0.01), and the receipt of immunosuppression prior to a blood culture draw (aOR 3.80, 95% CI 1.86-8.01, p < 0.001) were associated with an increased likelihood of speciating pathogenic Gram-positive bacilli from blood cultures such as Clostridium species and Listeria monocytogenes. Conclusion: Such predictors can help supplement a clinician's assessment on determining when empirical therapy is indicated when faced with Gram-positive bacilli from blood cultures and may direct future stewardship interventions for responsible antimicrobial prescribing.