Rapid Molecular Detection of Pathogens in 516 Consecutive Haematological Patients with Febrile Neutropenia

BACKGROUND: Febrile neutropenia and sepsis are frequent and life-threatening complications in patients with haematological malignancies. Although the proportion of infectious deaths in haematological patients has decreased over the last two decades, much remains to be done to further reduce these events. More effective preventive and prophylactic strategies for high-risk patients are necessary. Blood cultures (BC) identify a pathogen in only 20 to 30% of febrile episodes, the culturing and pathogen identification process is lengthy, postponing the start of a pathogen-targeted treatment. Thereby, a sensitive tool to promptly recognize pathogens causing sepsis is of high clinical relevance.

METHODS: We assessed the diagnostic usefulness of the LightCycler SeptiFast test (SF; Roche Molecular Systems), a PCR-based multiplex assay performed on peripheral blood and capable of detecting 25 among the most common species isolated in sepsis. The assay uses dual fluorescent resonance energy transfer (FRET) probes against the species-specific internal transcribed spacer (ITS) regions, a non-coding sequence interspaced among highly conserved bacterial and fungal RNA. Time from processing to result is remarkably short (less than 6 hours). In this study, blood samples from febrile haematological patients were concomitantly tested by traditional blood culture (BacT/Alert 3D; bioMerieux).

RESULTS: A total of 1941 blood samples were collected from 516 consecutive haematological patients treated for febrile neutropenia at the San Raffaele Haematology and Bone Marrow Transplantation Unit, from 2009 to 2013. Out of the total 1941 episodes examined, positive results were detected in 537 samples by SF (28%), and in 263 by BC (14%). Together, the two methods identified a total of 586 microorganisms in 509 (26%) episodes: Gram-positive bacterial species (80%), Gram-negative bacterial species (17%), and fungal species (3%). Concordance between the two methods was 77%, with most of the discordant samples that tested negative by culture but positive using the molecular approach (50% of the total positive samples). The cases positive by SF alone were mostly samples from patients already receiving antimicrobial therapy, or, importantly, sample positive for fungal pathogens such as Aspergillus fumigatus, which is hard to detect by the traditional approaches.

CONCLUSION: This analysis demonstrates a significant correlation between the molecular test and the standard BC in haematological patients with febrile neutropenia. A molecular test such as SF, in combination with traditional assays, can play an important role in the diagnosis of sepsis, particularly in persistent fever despite antibacterial therapy, when a non-responding bacterial infection or an invasive fungal infection is suspected, therefore leading to a rapid diagnosis and an earlier targeted antimicrobial therapy.