Contaminants in blood cultures: importance, implications, interpretation and prevention

Despite the development of new microbiologic technologies, blood cultures (BCs) remain the first-line tool for the diagnosis of bloodstream infections. Their diagnostic value may be affected when a microorganism of questionable evidence is isolated-for example, coagulase-negative staphylococci, Bacillus spp., viridans group streptococci, Corynebacterium spp., Propionibacterium spp. and Micrococcus spp. Finally, making a correct diagnosis of pathogenicity (vs. contamination) is challenging.

To review the current ways of dealing with the problem of BC contaminants (BCCs) and to provide practical suggestions to decrease BCC rates.

PubMed electronic databases and existing reviews were searched up to December 2017 to retrieve relevant publications related to the topic.

This review describes the burden of BCC and analyses the main current issues and controversies in interpreting the occurrence of potential BC contaminants. It focuses on the best-described approaches to decide whether BCC is present and discusses the different strategies of prevention in adults.

Each institution should have an efficient policy to prevent BCC, emphasizing the importance of following guidelines for prescribing and collecting BCs. Training healthcare workers should focus on detrimental influence on patient care and highlight the work and costs due to contaminants. The accurate differentiation of a contaminant from a true pathogen relies on a multidisciplinary approach and the clinical judgement of experienced practitioners.