Multi-pathogen real-time PCR system adds benefit for my patients: yes

Abstract

Need for the diagnosis of bloodstream infectionsBloodstream infections (BSI) are a major cause of death [1] and it is accepted that initiating an effective antimicrobial therapy in severe sepsis reduces mortality in a timely manner [2, 3]. In the era of increasing resistance, knowing pathogen and antibiotic susceptibility is critical for initiating appropriate antimicrobials [4, 5]. Unfortunately, microbial documentation of severe infections leading to BSI is still often overlooked and recognized too late for both technical and organisational reasons.Classical tools for diagnosing BSI are blood cultures (BC), i.e. collection of a large volume of blood (40 ml per episode) distributed into bottles and incubated at 35-37°C as soon as possible [6]. The time to result is long (2-3 days) because laboratories rarely work 24/7 and identification and antibiotic susceptibility testing are usually performed on subcultures [7]. Only 10 % of BC processed are positive and improving performance is a challenge [6, 7]. Moreover, patients often receive antimicrobials for therapeutic or prophylactic purposes, and BC positivity rates are lower unless specific bottles are used [4]. Molecular diagnosis of BSI appeared some years ago as a second option [5, 8]. Advantages of molecular detection are (1) shorter time to results [9] and (2) detection of non-cultivable microorganisms such as many fungi and bacteria under antibiotic pressure. However, the sensitivity of molecular tests is lower than that of cultures because the sample submitted to the test is much smaller (1.5 ml blood vs. 40 ml) and thus the limit of reproducible detection is about 30-100 colony forming units (CFU)/ml, compared to 1-10 CFU/ml for BC. Are blood cultures the gold standard for BSI?In a recent issue, Geoffrey Warhurst and colleagues measured the performance of the LightCycler Ò SeptiFast (LSF) test for patients with suspected healthcare-associated BSI [10]. They also performed a systematic review for determining STARD criteria of this test [11]. Warhurst et al. compared the LSF results to BC and concluded that the sensitivity of LSF was low (LSF positive in only 47 out of 80 BC-positive cases). Interference with human DNA and the presence of PCR inhibitors in the blood [12] might explain the false-negative LSF tests. However LSF was positive in many cases where BC was negative, but these cases were considered as false-positives since BC served as the gold standard. In the meta-analysis of 41 studies, summary sensitivity was somewhat higher (68 %) and specificity similar (86 %) to those in Warhurst's study [10]. These values are lower than those reported in the previous meta-analysis by Chang et al. who calculated 75 % sensitivity and 92 % specificity for 34 studies published until 2012, again taking BC as the reference [13].The main question is whether blood cultures can still be considered the gold standard, especially in healthcareassociated infections (HAI) where patients often receive antibiotics. Calculation of sensitivity with regard to Intensive Care ...

Performance and economic evaluation of the molecular detection of pathogens for patients with severe infections: the EVAMICA open-label, cluster-randomised, interventional crossover trial

“…It should be noted that in the previous studies, many cases were shown with positive molecular tests and BC-negative with clinical status showing signs of bloodstream infections [21, 22]. The cost-effectiveness of molecular direct testing in blood remains unknown [23]. …”

Real‐time PCR versus MALDI‐TOF MS and culture‐based techniques for diagnosis of bloodstream and pyogenic infections in humans and animals

“…2011), involvement of fastidious, slow growing, anaerobic or viable but non culturable (VBNC) bacteria (Al‐Tuffyli and Shekhan 2012); antibiotic pretreatment (Loonen et al . 2014) and the presence of intracellular pathogens which are phagocytized or only present in an infectious focus (Cambau and Bauer 2015).…”

Real -time PCR for early microbiological diagnosis: is it time?

“…On the other hand, blood cultures are less sensitive especially in the setting of recent exposure to antibiotics. Overall, blood cultures have only 70% specificity, and sensitivity *Correspondence: jarturpaiva@gmail.comis approximately 10% in suspected bacteremia, 30% in febrile neutropenia, 35% in severe sepsis, and 50% in septic shock [10]. Defining a true positive result for evaluating diagnostic tests for infection is challenging and may be best by a composite measure that includes clinical status and type and severity of infection.…”