Related Experiment Videos
False-positive blood cultures. Association with nonsterile blood collection tubes
Abstract:
A substantial increase in blood cultures positive for a Serratia marcescens strain unusually sensitive to antibiotics was noted in two large hospitals within six months. Because the patients' illnesses seemed incompatible with Serratia bacteremia, contamination of blood cultures was suspected. Investigation suggested that pediatric-sized vacuum tubes containing ethylenediamine tetraacetic acid (EDTA) were the source of the organisms, and the epidemic strain of Serratia was recovered from 41 (35%) of the 116 tubes cultured. Mock trials showed that reflux from tube to syringe can occur while vacuum tubes are being filled. Because contaminated EDTA tubes were sometimes inoculated before blood culture bottles in these hospitals, cross-contamination occurred. Most evacuated specimen tubes are not guaranteed sterile by the manufacturer. False-positive blood cultures stemming from the use of nonsterile tubes can be eliminated by inoculating blood culture bottles before other specimen tubes. Because false-positive blood cultures may lead to unnecessary antibiotic therapy, health-care workers should guard against the potential hazard associated with use of these tubes.
Insights
Contaminated EDTA vacuum tubes caused false-positive blood cultures for Serratia marcescens. Inoculating blood culture bottles first prevents this contamination, avoiding unnecessary antibiotic treatment.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Patient Safety
Background:
- An increase in Serratia marcescens bloodstream infections was observed.
- Patients' clinical presentations did not align with typical Serratia bacteremia.
Purpose of the Study:
- To investigate the source of increased Serratia marcescens blood culture positivity.
- To identify the cause of suspected blood culture contamination.
Main Methods:
- Culturing of pediatric vacuum tubes containing ethylenediamine tetraacetic acid (EDTA).
- Performing mock trials to assess potential for cross-contamination.
- Analyzing the sequence of tube inoculation in clinical practice.
Main Results:
- Serratia marcescens was recovered from 35% of tested EDTA tubes.
- Reflux from tube to syringe was demonstrated during filling.
- Cross-contamination occurred when EDTA tubes were inoculated before blood culture bottles.
Conclusions:
- Pediatric EDTA vacuum tubes were identified as the source of Serratia marcescens contamination.
- Nonsterile evacuated specimen tubes pose a risk for false-positive blood cultures.
- Inoculating blood culture bottles prior to other specimen tubes can prevent false-positive results and unnecessary antibiotic use.