Blood culture contamination rates in two district general hospitals in the Southeast of England

Introduction: Blood culture is considered an important diagnostic tool to identify the causative agent of bloodstream infection (BSI) as well as to direct the definitive therapy. High contamination rate in any healthcare institution is directly linked with increased cost, use of unnecessary antibiotics and additional testing in the diagnostic laboratories. The audit team determined the blood culture contamination rate and the distribution of microorganisms causing BSIs in patients for the East Sussex Healthcare Trust, United Kingdom. Materials and Methods: This is a retrospective study which analyses the blood culture results over 2 years period (January 2014 to December 2015). Positive blood cultures were grouped into significant, contaminant or unknown significance by reviewing patient clinical data collected at the time of positive blood culture and the microbiology records. Results: A total of 11036 blood cultures were processed in the microbiology laboratory during the study (January 2014 to December 2015). A total of 1641 (14.9%) blood cultures were positive. Of 1641, 1298 (11.8%) and 286 (2.6%) were grouped as significant and contaminant, respectively. Fifty-six positive blood culture sets remained indeterminate due to the lack of the clinical information. The overall contamination rates in both hospitals in 2014 and 2015 were 0.9% and 1.7%, respectively. The average yearly contamination rate is 1.3%. Higher contamination rates were recorded from the paediatric, emergency, orthopaedics and surgical departments. A total of 1753 microorganisms were isolated. The most common isolated organisms include Escherichia coli 482, (27.5%), Coagulase-negative Staphylococcus, 274 (15.6%), Streptococcus species, 183 (10.4%), Staphylococcus aureus, 162 (9.2%), Klebsiella species, 135 (7.7%), Enterococcus species, 109 (6.2%) and Streptococcus pneumonia, 48 (2.7%). Thirty-three Candida species were isolated. The prevalence of methicillin-resistant S. aureus and the extended-spectrum b-lactamase producing Enterobacteriaceae were low. Conclusion: The present data showed lower contamination rate in the Trust than the acceptable rates. It also supports the need for regular training and education of healthcare professional that collect blood culture where the contamination rates are high.