Background Blood culture contamination can have many negative effects including unnecessary treatments, costs and contribution to antibiotic resistance. Neonates are often treated on the basis of a single blood culture result, so minimising contamination rates is very important.
Aim To retrospectively study blood culture contamination rates and the impact of improving sterility of sample collection in a tertiary neonatal unit. The correlation between rates of central line associated bloodstream infection (CLABSI) and blood culture contamination rate will also be analysed.
Methods All blood cultures taken between January 2012 and September 2013 were studied. Sterile pack use for sample collection was introduced from November 2012. The difference in blood culture contamination rates before and after introduction of the sterile pack was analysed using the two tailed independent t-test.
Findings The overall blood culture contamination rate was 5.08%. Improvement of sample collection sterility decreased contamination rates by 41.7%, from 6.51% to 3.83% (p = 0.07). Of all positive blood cultures, 56.25% were due to contamination. Coagulase negative staphylococcus (CoNS) was present in 87.67% of contaminated blood cultures, with 66.10% of CoNS positive samples representing contamination. The Pearson correlation coefficient of -0.385 suggests a moderate negative correlation between CLABSI and blood culture contamination rates.
Conclusions Improving aseptic techniques of sample collection reduced blood culture contamination rates on our unit. Positive blood cultures should be interpreted carefully, as over half were due to contamination. The possible negative correlation between CLABSI rate and blood culture contamination could be explained by small sample size and needs further study.