Clinical Impact of Rapid AST Directly From Blood Cultures

Overview

Bacteremia is defined as pathogenic bacteria presence in blood as evidenced by positive blood cultures. These bacteremia have significant consequences in terms of morbidity and mortality (ref. 1,2,3). They can lead to a state of septic shock that is life-threatening for the patient and must be treated as a matter of urgency. Any delay in treatment is detrimental to the patient. Management is based on prescription of probabilistic antibiotic therapy as soon as bacteremia is suspected. At the Groupe Hospitalier Paris Saint Joseph (GHPSJ), as soon as a blood culture is known to be positive, the Mobile Clinical Microbiology Unit (UMMC) is notified in real time. The UMMC infectiologist, in consultation with the microbiologist, evaluates microbiological data and compares them with clinical data in order to prescribe probabilistic antibiotic therapy in the patient's bed. The possible adaptation of antibiotic treatment then depends on the results of antibiotic susceptibility test. Early adaptation of antibiotic treatment to antibiotic susceptibility data, to reassess ineffective treatment or to reduce antibiotic therapy spectrum, significantly improves patient prognosis: it is therefore important that the laboratory makes antibiotic susceptibility test results available to the clinician as early as possible.

The standard method based on diffusion on agar medium on conventional CBM allows antibiotic susceptibility results the test to be rendered within 24 hours. Many so-called rapid methods (Accelerate PhenoTM system, VITEK 2 Rapid Identification and Susceptibility Testing System,...) have been developed to improve antibiotic susceptibility testing speed from positive blood cultures. However, these approaches are costly and not exhaustive in terms of antibiotic panels tested. The Mueller-Hinton Rapid-SIR (MHR-SIR) i2a medium has been developed. It is an agar medium allowing an early reading of antibiotic susceptibility test due to contrasting agents presence in culture medium which facilitates antibiotic susceptibility test results reading in less than 8 hours on a majority of fast-growing bacteria, in particular Enterobacteriaceae and golden staphylococci. A prospective evaluation of the Mueller-Hinton Rapid-SIR (MHR-SIR) medium's performance directly from blood cultures was conducted in GHPSJ laboratory and published in 2018 with very satisfactory results obtained in less than 8 hours with a correlation \> 97% compared to the standard MH method (Results published in DMID ref.5) at a very moderate cost of 5 euros for 16 antibiotics in free choice; The additional cost compared to the traditional MH is 20% or 0.4 euros per agar. In view of excellent results of the study, this technique has replaced the traditional MH technique in GHPSJ laboratory since January 2017, allowing UMMC to propose more quickly adaptations of probabilistic antibiotic therapy. The use of the MHR-SIR medium has never been evaluated in a clinical context. The objective of this pioneering study is to routinely evaluate the rendering clinical impact of the rapid antibiotic susceptibility test MHR-SIR (i2a) after 8 hours of incubation directly from the blood cultures.