The opening and closing of empiric windows: the impact of rapid microbiologic diagnostics.

TO THE EDITOR—With the advent of rapid diagnostic techniques for pathogen identification, clinicians are encountering increasing windows of time when they are aware of an infecting organism’s species without yet knowing its susceptibilities [1, 2]. We believe that it is worthwhile to formally recognize these empiric windows in the management of infectious diseases (Figure 1). These windows include infectious syndrome–guided therapy (empiric window 1), Gram stain morphology–guided therapy (empiric window 2), and pathogen-guided therapy (empiric window 3), before, finally, susceptibility-guided therapy. Rapid speciation methods including matrix-assisted laser desorption/ionization–time of flight, and, potentially, polymerase chain reaction–based methods, could close the empiric window 2 by half (from 54 to 24 hours), while opening empiric window 3 much more widely (from 3 hours up to 21 hours) [1, 2, 4]. The alteration of these empiric windows can have significant impact on patient outcomes and may pose new challenges for treating physicians. Empiric window 2 has historically been a critical time period where clinicians may adapt their treatment approach based on Gram staining. Having less time between the Gram stain and pathogen identification may lead clinicians to wait for speciation results rather than having to make more frequent antimicrobial changes. Empiric window 3, traditionally a small window between speciation and susceptibility results, will be increased with rapid speciation techniques, and this means that clinicians have time to adapt their empiric therapy accordingly. This will suddenly make institutional species-specific antibiograms much more clinically useful. Moreover, clinicians may be able to more quickly discontinue therapy following identification of obvious culture contaminants (eg, Corynebacterium species), or more rapidly de-escalate therapy after identification of organisms with predictable susceptibilities (eg, Listeria monocytogenes). In some instances, empiric window 3 will cause pathogen-guided escalation prior to susceptibility-guided de-escalation of empiric therapy (eg, Enterococcus species or Pseudomonas species) [1].