Diagnostic techniques in bloodstream infections: where are we going?

Rapid and early detection of bacteria in blood has an important role in the diagnosis of a febrile patient for at least three reasons: to establish the presence of an infection, to reassure the clinician about the chosen empirical therapy and to define antibiotic treatment after isolation of the microorganism and determination of its antibiotic susceptibility. We all agree that blood culture is the gold standard for aetiological diagnosis. However, it has limitations: the time required for bacteria to multiply to a detectable number of cells, the inadequate sensitivity of blood culture for fastidious pathogens and in patients who have previously received antibiotics, or when there is a catheter-related bloodstream infection. We must, however, remember that the current blood culture data constitute an important epidemiological tool on which clinicians can base empirical therapy. Over the past few years many new molecular tests have been developed that are now entering mainstream practice. These tests are more rapid, specific and sensitive; however, there are still some problems: antibiotic susceptibility testing is still lacking, and sometimes they are so sensitive that a skilled operator may be necessary for an accurate interpretation of the results. These new methods are promising, and their performance can only get better as they are increasingly used in clinical microbiological laboratories.