(636) The CoNSequences of Blood Culture Contamination With Coagulase-Negative Staphylococcus

Introduction: Blood culture contamination (BCC) represents an ongoing source of frustration for clinicians, as up to 50% of positive blood cultures are identified as contaminants, with Coagulase Negative Staphylococcus (CoNS) representing 88% of the contaminants. The complications of BCC include unnecessary antimicrobial treatment, promote development of antimicrobial resistance, adverse drug effects and increased length of stay, which ultimately increase cost of care. The purpose of this multidisciplinary study is to assess the prevalence and consequences associated with CoNS BCC.

Methods: This is a single-center, retrospective chart review, conducted at Ascension St. John Hospital, in Detroit, Michigan. A total of one-hundred adults with positive CoNS blood cultures, between January 1, 2018, and August 24, 2023, was collected from the inpatient electronic medical record. Patients were excluded if definitive gram-positive antibiotic treatment was required, other than for CoNS. True infection was defined as CoNS blood cultures treated with antibiotic therapy duration for five days or longer per Infectious Disease Specialist recommendations. All other CoNS cultures was considered BCC. The consequences evaluated include vancomycin doses administered, vancomycin levels obtained, subsequent blood cultures obtained, infectious diseases consultation, pharmacy to dose consultation, and adverse drug effects.

Results: CoNS BCC is above the Clinical and Laboratory Standard institute (CLSI) recommended contamination rate of < 3%, with about 63% being contaminants. BCC led to unnecessary use of antimicrobials in 67% of patients with average of 2 doses of vancomycin received per patient. This led to unnecessary vancomycin levels obtained in 41% of patients with an average of 1 level obtained per patient. Forty-six percent of BCC led to subsequent blood cultures draws, with only 3% resulting as positive. Infectious disease was consulted on 87% of BCC patients, leading to 57% obtaining a pharmacy to dose consults. Acute kidney injury occurred in 38% of BCC patients after vancomycin treatment.

Conclusions: The prevalence of CoNS BCC was high at our institution, which led to unnecessary vancomycin use, which may contribute to antimicrobial resistance. It also led to unnecessary resource utilization and adverse drug effects.