Division of Infectious Diseases

Clinical Consequences of Contaminated Blood Cultures in Adult Hospitalized Patients at an Institution Utilizing a Rapid Blood-Culture Identification System

Dr. Mark Rupp; senior author and Division Chief for @UNMC_ID

Blood culture contamination results in prolonged hospital length of stay, inappropriate use of antibiotics, and increased cost as well as the associated adverse events such as falls, drug errors, and healthcare associated infections (adverse events that may occur during more prolonged hospital stay) and emergence of antibiotic resistance, C. difficile infection, and antibiotic side effects (adverse events associated with unnecessary antibiotic administration).

However, nearly all studies indicating the harm associated with blood culture contamination were performed in the era prior to the use of rapid, molecular-based blood culture identification systems. In many instances, with use of rapid blood culture ID systems, true pathogens can be differentiated from likely contaminants (e.g. Staphylococcus aureus versus coagulase-negative staphylococci) very quickly. The effect of rapid blood culture ID systems on the clinical importance of blood culture contamination is not well described.

Therefore, we performed a large retrospective cohort study comparing outcomes between hospitalized patients with blood culture contamination and those with sterile blood cultures – during a time period when a rapid blood culture identification system (Biofire FilmArray Blood Culture Identification) was in routine use.

From June 1, 2014 to December 31, 2016, 19,255 patients were admitted to the hospital who had blood cultures performed. After excluding pediatric age patients, patients with true bacteremia, patients with repeated admissions, and those with equivocal results, we analyzed outcomes in 11,010 patients with sterile cultures and 464 with contaminated cultures. Primary outcomes of interest were hospital length of stay and antibiotic use. Variables potentially affecting outcome were examined and included socio- demographic factors (age, gender, race, marital status, medical insurance status) and various comorbid conditions including smoking, alcohol use, BMI, COPD, CKI, cirrhosis, and diabetes. Additional factors examined included ICU stay, admission from the emergency department, and location of blood draw (peripheral vein versus central venous catheter).

Univariate and multivariate analysis was conducted using generalized linear models. Forward stepwise selection was utilized to create the final model and Akaike information criterion value was used to assess model fit.

Bottom line, after controlling for age, gender, race, BMI, comorbid conditions, and hospital factors, blood culture contamination was associated with nearly a full extra day (0.8 days) of hospital stay (P= 0.032) and nearly a full day (0.8 days) of unneeded antibiotics (P= 0.011).

Previous studies have noted the adverse effect of blood culture contamination on clinically important outcomes, and in general, previous investigators noted a greater effect then was noted in our study. The decreased negative effect may be due to the use of rapid blood culture identification systems and the presence of a robust antimicrobial stewardship program at our institution.

Therefore, despite the use of molecular-based rapid blood culture identification systems and well-functioning antimicrobial stewardship programs, blood culture contamination continues to adversely impact patient outcomes – resulting in significantly prolonged hospital stay and unnecessary use of antibiotics. Efforts to minimize blood culture contamination continue to be justified and needed!

Sidra Liaquat MBBS, MSc, Lorena Baccaglini PhD, DDS, Gleb Haynatzki PhD, DSc, Sharon J. Medcalf PhD and Mark E. Rupp MD

Infection Control & Hospital Epidemiology (2020), 1–7. doi:10.1017/ice.2020.1337




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