Diagnostic accuracy and clinical impact of loop-mediated isothermal amplification for rapid detection of Staphylococcus aureus bacteremia: a retrospective observational study

The aim of this study was to evaluate the diagnostic accuracy and the clinical impact of isothermal loop-mediated amplification (LAMP; eazyplex® MRSA kits) for rapid diagnosis of Staphylococcus aureus bacteremia (SAB) in comparison with conventional blood culture diagnostics. We performed a retrospective, single-center observational study over the period between November 2016 and December 2018 on patients (and blood cultures) with growth of Gram-positive cocci in clusters in their blood cultures. We quantified diagnostic accuracy with sensitivity and specificity for detection of S. aureus, methicillin-resistant S. aureus (MRSA), and the mecA/C resistance genes in 797 blood cultures. The clinical impact was assessed by time to result reporting, time to appropriate treatment, and length of stay in intensive care unit (ICU) in 190 SAB patients. We observed sensitivity and specificity above 90% for S. aureus detection (sensitivity (95% confidence interval (CI)), 99.57% (97.61%, 99.98%); specificity, 99.12% (97.95%, 99.71%)), for MRSA detection (sensitivity, 100% (89.11%, 100.00%); specificity, 99.72% (99.05, 99.96)), and for mecA/C detection (sensitivity, 94.71% (91.85%, 96.78%); specificity, 95.89% (93.58%, 97.54%)). LAMP testing was associated with shorter median time to result reporting (24.0 h (first and third quartiles (Q1–Q3), 20.0–27.0 h) vs 41.5 h (36.0–46.0 h); p < 0.001) and different distribution of time to appropriate treatment (2.0 days (1.0–3.0) vs 2.0 days (2.0–3.0); p = 0.004). No evidence for differences in length-of-stay in ICU was observed. Our analysis suggests for the application of LAMP (i) a high diagnostic accuracy for detection of S. aureus and the mecA/C genes in blood cultures, (ii) an earlier result reporting, and (iii) a shorter time to appropriate treatment.