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578: USE OF COMPLETE BLOOD COUNT SUBGROUP PARAMETERS IN PREDICTING S AUREUS BACTEREMIA MORTALITY

Introduction/Hypothesis: Staphylococcus aureus bacteremia (SAB) mortality is high despite effective antibiotic therapy and rapid diagnostics. Various cytokine measurements are associated with increased SAB mortality. Clinical use of these biomarkers is uncommon due to availability and cost. The complete blood count (CBC) with differential provides an alternative reflection of the host immune response. There exist a paucity of data examining the relationship between the CBC subgroup parameters and SAB outcomes. Methods: This retrospective, observational cohort included patients ≥18 years of age in 16 Wisconsin hospitals with SAB and an infectious disease consult between June 1 and November 16, 2016. Clinical and microbiologic data were collected. Illness severity was determined using the PITT bacteremia score. Each patient’s white blood cell count, neutrophil count, lymphocyte count, neutrophil to lymphocyte count ratio (NLCR), eosinophil count, platelet count and red blood cell distribution width were recorded on the first day of SAB. The primary outcome was 30-day, all-cause mortality. A multivariable logistic regression model was used to determine the association between patient variables and mortality. Results: 119 patients were included. 53 patients were directly admitted to the ICU. Overall mortality was 10.1%. The median NLCR ratio in the mortality group was 23.2 vs 13.6 in the survival group (p=0.0074). The median lymphocyte count in the mortality group was 0.6 vs 0.9 x 10 cells/μL in the survival group (p=0.03). The median platelet count was lower in the mortality group compared to the survival group, 171 vs 239 x 10 cells/μL, respectively (p=0.0175). All other CBC subgroup parameters were similar between the two groups. Known predictors of SAB mortality such as congestive heart failure, endovascular infection source and elevated PITT bacteremia score were associated with mortality. Low lymphocyte count was independently associated with mortality (adjusted odds ratio [aOR] 0.236, 95% CI 0.064-0.872) as was PITT bacteremia score (aOR 2.439, 95% CI 1.565-3.803). Conclusions: Various CBC subgroup parameters may have prognostic value in SAB. Additional study, with a larger sample, is warranted to further ascertain the prognostic value of these readily available laboratory values.