Although technological improvements have led to reductions
in the time required for identification and (in limited cases)
susceptibility testing of isolates from signal-positive blood
cultures, a further improvement would obviously be the ability
to rapidly and directly detect and identify microorganisms in
blood samples from patients with a suspected BSI. Currently
available solutions involve the use of NAATs that are designed
to detect specific microorganisms in blood samples [68].
Controlled trials evaluating the performance of such solutions
as compared with standard blood cultures have demonstrated
reasonably good performance, with the obvious limitation that
NAATs will only detect a subset of possible BSI pathogens,
and provide no susceptibility information [68,69]. As conventional
phenotypic susceptibility testing requires isolated
organisms, if the direct NAAT is positive and the corresponding
culture is negative, susceptibility information may never be
available. Thus, at the present time, such an approach may
serve only as an adjunct to standard of care protocols. As is
the case for rapid methods for blood culture isolate identification,
the actual clinical impact of rapid methods for direct
pathogen detection in blood specimens has not been extensively
studied.