Reducing blood culture contamination in the emergency department through changes in sampling technique: an...

Following the implementation of a national guideline recommending two blood culture sets for patients with suspected sepsis, routine surveillance in our large tertiary emergency department identified increased contamination. We aimed to identify contributory sampling practices and evaluate a co-produced intervention to reduce contamination.

We conducted a two-phase quality improvement project. In phase one, blood cultures were prospectively labelled by sampling technique and compared by χ² testing. In phase two, a multi-disciplinary team co-produced an intervention eliminating the technique most associated with contamination. Monthly contamination proportions were analysed using quasi-binomial interrupted time-series regression, modelling step, and slope changes at both guideline introduction and the intervention. Safety analyses examined effects on sampling rates, underfilled sample rates, and true bacteraemia detection.

We analysed 20,263 blood cultures (January 2022-June 2025). The guideline's introduction was associated with an immediate rise in contamination (odds ratio [OR]: 1.56, 95% confidence interval [CI]: 1.15-2.12; P=0.005). Cannula-and-syringe sampling had higher contamination than other methods (25/238 [10.5%] vs 3/157 [1.9%]; P=0.002). Withdrawal of this method led to an immediate reduction (OR: 0.49, 95% CI: 0.36-0.66; P<0.001) without reversion over time, corresponding to a decrease from 12.3% (95% CI: 9.0-16.6%) to 6.8% (95% CI: 5.8-7.9%). Sampling rates, underfilled sample rates, and true bacteraemia detection were unchanged.

Sampling method is a major contributor to blood culture contamination. Avoiding cannula-and-syringe sampling reduced contamination, without compromising diagnostic yield. Departments implementing two-set blood culture policies should monitor contamination and consider targeted mitigation.