Defining microbial invasion of the bloodstream: a structured review

Background: Microbial invasion of the bloodstream is associated with a major burden of illness. Despite its importance, there is inconsistency in utilization of terms used to define it. Objective: To characterize the contemporary use of terms to define microbial invasion of the bloodstream for surveillance and research purposes. Methods: Structured review of publications reported from 2000 to 2019. Results: The search strategy retrieved 10,095 citations of which bloodstream infection, bacteraemia and fungaemia were included in 2813, 6900 and 1054 articles, respectively. There was a tripling of the number of annual citations during the study and although bacteraemia was most frequent, there was a progressive increase in the use of the term bloodstream infection. Among the 100 reports randomly selected for detailed review, the terms bacteraemia, bloodstream infection and fungaemia were used in 57, 51 and 19 publications, respectively. Explicit definitions for bloodstream infection (26/51; 51%), bacteraemia (13/57; 23%) and fungaemia (7/19; 37%) were included in reports where these terms were used. Although nearly all (95%) of the studies indicated a positive blood culture as an inclusion criteria and/or definition, only a minority indicated means to exclude contaminants (33%) or specific attributes to support clinical significance (38%). Use of explicit definitions was more common among reports that exclusively used the term bloodstream infection as compared to bacteraemia. Conclusions: Terms have been inconsistently defined and imprecisely used to refer to microbial invasion of the bloodstream. Clinically relevant and objective definitions that are widely acceptable are needed for surveillance and research purposes.