Usefulness of real-time polymerase chain reaction for the diagnosis of intensive care unit-acquired infections

Abstract

Real-time polymerase chain reaction (PCR) methods are able to rapidly detect a wide panel of microorganisms. These methods are of interest in critically ill patients to determine the presence of bacteria in blood samples, especially in patients with prior antimicrobial treatment. In the intensive care unit (ICU), the most frequently used kit is the LightCycler® SeptiFast (LC-SF) Test providing 1.5- to 2-fold higher positivity rate compared with conventional blood cultures. Although identification of the bacterium by LC-SF is rapid and sensitive, susceptibility test can not be performed using this technique, except for methicillin-resistance of Staphylococci. Thus conventional cultures remain necessary for blood samples due to the high incidence of multidrugresistant bacteria in the CIU and the need of antimicrobial susceptibility in order to initiate appropriate antimicrobial treatments. A negative result for a Gram positive or negative bacterium could allow deescalating the initial antimicrobial treatment, decreasing the pressure of selection. Moreover, it is necessary to the clinicians to understand and interpret a deoxyribonucleic acid (DNA) signal knowing that a dead bacterial material may be detected in a patient without any infection. What is the clinical relevance of bacterial DNA present in the blood? Does the DNAemia reflect a true infection? Does a positive DNA signal without positive blood cultures correspond to an unfavorable outcome? Cost-effectiveness of the real-time PCR should be investigated. Meanwhile, this test should be restricted to severe clinical situations, especially to ICU patients with severe sepsis. In the future, real-time PCR tests should include more pathogens and antimicrobial resistance targets.