A Need to Also Consider Divergence in the Definition of Staphylococcus aureus Bacteremia Free

To theEditor—I enjoyed reading Westgeest et al's article in which they describe the widespread divergence in the management of Staphylococcus aureus bacteremia (SAB) globally [1]. I would note that the lack of an international standard of care for SAB is further hampered by the lack of an accepted diagnostic criteria for SAB.

As a common skin commensal, S. aureus can be a cause of pseudo-bacteremia as well as true bacteremia. The willingness to attribute S. aureus in blood cultures to sampling contamination varies widely. Given the potentially devastating complications of untreated, true SAB, “contamination” is anathema to some authorities [2, 3]. Other studies attribute SAB to blood culture contamination in 2.5% [4], 4% [5], and 6% [6] of adult episodes, with higher rates in children (9.5% [7]; 20% [8]). None clearly define the criteria that constitute contamination.

Microbiology diagnostics have become progressively more sensitive since the first SAB studies were published in the 1950s. Modern automated blood culture analyzers can detect very small numbers of bacteria, whether truly present in the bloodstream or inadvertently introduced into blood culture bottles. SAB may not therefore be exactly the same disease entity it was some decades previously. Whether due to contamination or transient bacteremia, patients with S. aureus in blood cultures can remain clinically well and have good outcomes despite no or minimal antimicrobial treatment [9]. The risk of exposing persons without true bacteremia to at least 14 days of antimicrobials, venous access, and source investigation procedures is not entirely benign. Inclusion of such patients in clinical trials brings in a potential confounding factor in interpreting outcome data, as they would be expected to have a good outcome irrespective of the intervention under study. These patients, however, are hard to characterize and real risk remains where an attribution of contamination is erroneously made. Before an international standard of care can be agreed on, it is perhaps first necessary to tackle the thorny issue of what defines a “true” S. aureus bacteremia.

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Author notes