BackgroundEarly diagnosis and rapid bacterial identification are of primary importance for outcome of septic patients. SeptiFast® (SF) real-time PCR assay is of potential utility in the etiological diagnosis of sepsis, but it cannot replace blood culture (BC) for routine use in clinical laboratory. Procalcitonin (PCT) is a marker of sepsis and can predict bacteremia in septic patients. The aim of the present study was to investigate whether PCT serum levels could predict SF results, and could help screening febrile patients in which a SF assay can improve the etiological diagnosis of sepsis.MethodsFrom 1009 febrile patients with suspected sepsis, 1009 samples for BC, SF real-time PCR, and PCT determination were obtained simultaneously, and results were compared and statistically analysed. Receiver operating characteristic (ROC) curves were generated to determine the area under the curve and to identify which cut-off of PCT value produced the best sensitivity to detect SF results.ResultsMean PCT values of sera drawn simultaneously with samples SF positive (35.42±61.03 ng/ml) or BC positive (23.14±51.56 ng/ml) for a pathogen were statistically higher than those drawn simultaneously with SF negative (0.84±1.67 ng/ml) or BC negative (2.79±16.64 ng/ml) samples (p<0.0001). For SF, ROC analysis showed an area under the curve of 0.927 (95% confidence interval: 0.899–0.955, p<0.0001). The PCT cut-off value of 0.37 ng/ml showed a negative predictive value of 99%, reducing the number of SF assays of 53.9%, still identifying the 96.4% of the pathogens.ConclusionPCT can be used in febrile patients with suspected sepsis to predict SF positive or negative results. A cut-off value of 0.37 ng/ml can be considered for optimal sensitivity, so that, in the routine laboratory activity, SF assay should not be used for diagnosis of sepsis in an unselected patient population with a PCT value <0.37 ng/ml.

Early detection of aetiological agents is pivotal for adequate therapy for bacterial infections. Although culture is still considered the mainstay for laboratory diagnosis, it often lacks sensitivity, especially in patients already treated with antibiotics. The present study investigated the potential clinical utility of the commercial real-time-PCR-based system SeptiFast (SF), originally intended for diagnosis of sepsis from blood specimens, in the aetiological diagnosis of other bacterial infections, in patients undergoing antibiotic therapy. A total of 53 non-blood specimens were analysed for microbial pathogen detection by conventional culture and with SF real-time PCR: 19 (35.8 %) synovial fluids, 9 (17.0 %) cardiac valve tissues and 25 (47.2 %) purulent exudates from various body sites. Overall, the number of specimens positive for a pathogen by SF (26/53; 49.1 %) was significantly greater (P50.001) than that of specimens positive by culture (10/53; 18.9 %). In particular, SF was superior to culture for pathogen detection in cardiac valve tissues and synovial fluids. The analysis of concordance showed a fair agreement between the two methods (kappa value50.314; 95 % confidence interval50.531-0.097). Even with the limitation of the low number of specimens, this study confirmed the great potential of diagnosing bacterial infections by a molecular approach, and indicates that the real-time PCR SF system can be used for specimens other than blood, from patients undergoing antibiotic treatment.

JMM CorrespondenceDiagnosis of infective endocarditis: comparison of the LightCycler SeptiFast real-time PCR with blood culture

Valutazione del sistema GeneXpert ® per la rilevazione di Staphylococcus aureus meticillinoresistente in campioni clinici SUMMARY Infections caused by methicillin-resistant Staphyloccocus aureus strains (MRSA) have reached epidemic proportions globally, being the major cause of nosocomial infections. Rapid identification of MRSA in nasal swabs or in clinical samples is considered a useful strategy for control and treatment of these infections. GeneXpert system (Cepheid Europe,Vira-Solelch, Maurence-Scopont-France) can detect by real-time PCR in approximately one hour methicillin-resistant S. aureus or coagulase-negative staphylococci (CoNS) in clinical samples, in comparison with 24 hours for the culture or 48 hours for the antimicrobial susceptibility testing. In this study GeneXpert system was compared with traditional tests for MRSA detection in nasal swabs, bloodcultures and surgical wound swabs. Materials and methods. Eighteen nasal swabs, 23 blood-cultures and 13 surgical wound swabs were tested. The samples were cultured on blood-agar and mannitol-salt agar. Identification of isolates was carried out with traditional tests (Gram staining, catalase, coagulase) and automatic Phoenix system. Methicillin-susceptibility was evaluated according to 2010 CLSI guidelines. GeneXpert system was performed according to manufacturers instructions, by using the specific kits and methicillin-resistance was detected by amplification of the genic sequences spa, SCC e mecA. Results. The results showed a 100% accordance between GeneXpert system and traditional tests for detection of methicillin-resistant staphylococci. In particular, among 18 nasal swabs, no MRSA was detected, while 1 bloodculture (4.3%) and 4 surgical wound swabs (30.7%) were positive for MRSA. Conclusions. GeneXpert system allows a rapid detection of MRSA in clinical samples and shows the same sensitivity and specificity as traditional tests. Therefore, it represents a further effective diagnostic method for prevention and treatment of nosocomial infections due to methicillin-resistant staphylococci.

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