Quality assurance in blood culture: A retrospective study of blood culture contamination rate in a tertiary hospital in Nigeria

BACKGROUND: Blood culture is a critical tool for diagnosing septicaemia. Quite frequently, contamination of blood sample poses a great challenge to accurate diagnosis. This study evaluated the rate of blood culture contamination in our hospital over a one-year period. MATERIALS AND METHODS: It was a retrospective study of 1032 blood cultures carried out in a clinical laboratory of a tertiary hospital in North Central part of Nigeria between 2010 and 2011. RESULTS: There were 730 blood cultures from paediatric and 302 adult patients. The overall yield was 22%; 107 out of the 730 were contaminated giving a contamination rate of 10.4%. Contamination rate was higher in children than in adult (11% vs 8%) specimen. These rates were much higher than the acceptable benchmark of 2-3%. The main contaminants were coagulase negative Staphylococcus, Bacillus species, Diphtheroids and Enterococcus species. CONCLUSION: Contamination rate is high, and mainly due to normal skin flora, suggesting aseptic collection challenges as the main cause. We recommend a review of the entire process of blood collection for culture and analysis with a view to instituting appropriate quality assurance measures to reduce the contamination rate.