Etiological diagnosis of bloodstream infections through a multiplex real-time polymerase chain reaction test in pediatric patients: a case series from a tertiary Italian hospital.

Background: The outcome of bloodstream infections (BSIs) is strongly related to microbiological diagnosis. Several factors may reduce blood culture (BC) diagnostic yield in pediatric BSIs, making the application of molecular methods quite promising.

Methods: Multiplex real-time polymerase chain reaction (PCR) tests (the LightCycler Septifast Test MGRADE by Roche Diagnostics--LC-SF) performed in the tertiary centre of Regina Margherita Children's Hospital (Turin, Italy) over a 3-year period were retrospectively evaluated. Results of the LC-SF test were compared with those of BC (Automated Bact/Alert 3D, Biomerieux) collected at a close time point.

Results: 545 LC-SF tests were collected from 289 patients (183 males, median age 6.8 years, interquartile range (IQR) = 2.7-13.1); 163 had congenital or acquired immunodeficiency. In 515 cases (94.5%) the LC-SF test was performed with ongoing empirical antimicrobial therapy. Etiological definition was achieved in 111 BSI cases (20.4%). Both LC-SF and BC identified the responsible pathogen in 39 episodes. The LC-SF test alone gave a positive result in 29 septic episodes; BC alone permitted the etiological diagnosis in 43 episodes, but isolates were not included in the LC-SF master list in 10 cases. A 26% increase in bacterial identification chances due to the LC-SF test was documented. Cohen's kappa test indicated a moderate strength of agreement (0.49) between LC-SF tests and BCs closely collected.

Conclusions: BC remains the gold standard for the etiological diagnosis of BSIs, but PCR methods proved to be a valuable adjunctive diagnostic tool in pediatric BSIs, especially in children receiving empirical chemotherapy.