Summary: In one of the most comprehensive evaluations of its kind, Fabre et al. (2025) show striking variability in how hospitals define, measure, and act on blood culture contamination data, highlighting the need for national standardisation of definitions and reporting metrics.
Study on Reporting Blood Culture Contamination Metrics
Why This Matters:
- Blood culture contamination (BCC) leads to false-positive results that can trigger unnecessary antibiotic use, inflate central-line–associated bloodstream infection (CLABSI) rates, and distort hospital performance metrics.
- CLSI recommends a contamination threshold of <3%, with ≤1% considered optimal—but no standardized national definition exists, resulting in significant reporting variability.
- By comparing three major classification systems which differ by defined skin commensals - College of American Pathologists (CAP), CLSI, and National Healthcare Safety Network (NHSN) - this study shows that the choice of definition alone can significantly change reported BCC rates.
- Findings also identify modifiable institutional practices, including data transparency and blood culture source that directly influence contamination rates.
Key findings: Kenney et al. (2025) analyzed 362,078 blood culture sets collected between September 2019 and August 2021 across 48 hospitals.1
- Definition variability:
- Hospitals used CAP (65%), CLSI (17%), and NHSN (17%) criteria to define contamination.
- BCC (Blood Culture Contamination) rates averaged 1.38% in ICUs and 0.96% on wards using CAP definitions - similar under CLSI, but markedly higher when the broader NHSN commensal list was applied.
- Monitoring practices:
- All hospitals tracked BCC rates but only 39% monitored positivity rates and 21% tracked single-bottle collections in a 24h period rates, leaving key quality indicators unmeasured in most cases.
- Associated factors:
- Lower BCC rates correlated with sharing BCC data beyond the microbiology laboratory, tracking multiple quality indicators, and restricting cultures drawn from central lines.
- Higher BCC rates were associated with increased Central Line-Associated Bloodstream Infection incidence in ICUs and greater vancomycin utilization, underscoring clinical and stewardship implications.
References:
1. Fabre et al. (2025).“Multicenter evaluation of blood culture contamination and blood cultures practices in US acute care hospitals: time for standardization.” Journal of Clinical Microbiology. Vol. 63, Issue 8 (2025): e0053025.
2. Bunn et al. (2025). “Blood Culture Contamination and Diagnostic Stewardship: From a Clinical Laboratory Quality Monitor to a National Patient Safety Measure.” The Journal of Applied Laboratory Medicine. Vol. 10, Issue 1: 162-1702
