Rapid Detection of Pathogens Causing Sepsis in Neutropenic Hematologic Patients by a Multiplex PCR-Based Assay

Febrile neutropenia and sepsis are frequent and life-threatening complications in patients with hematological malignancies. Prompt administration of appropriate antimicrobials is crucial to decrease the high morbidity and mortality rates of these conditions. Blood cultures (BC) identify a pathogen in only 20 to 30% of febrile episodes, with even lower sensitivity in patients already receiving antibiotics at time of sampling. Moreover the culturing and pathogen identification process is lengthy, postponing the start of a pathogen-targeted treatment, a particularly relevant issue when highly aggressive or rare agents are involved. Thereby the setup of molecular tools able to promptly recognize pathogens causing sepsis even despite ongoing antimicrobial therapy is of potential clinical relevance.

We assessed the diagnostic usefulness of the LightCycler SeptiFast test (SF), a PCR-based multiplex assay which can be performed on peripheral blood in hematological patients. In this study, blood samples from febrile oncohaematological patients were tested by traditional blood culture (BacT/Alert 3D; bioMerieux) and by a novel commercial real-time PCR assay (LightCycler SeptiFast; Roche Molecular Systems) performed concomitantly at the onset of febrile neutropenia.

A total of 869 blood samples were collected from 273 consecutive patients treated for febrile neutropenia at the San Raffaele Hematology Unit over the last three years (July 2009–July 2011). Out of the total 869 episodes examined, positive results were detected in 246 samples by SF (28.3%), and in 143 by BC (16.4%). Together, the two methods identified a total of 345 microorganisms in 312 (36%) episodes: Gram-positive bacterial species (74%), Gram-negative bacterial species (23%), and fungal species (3%). Concordance between the two methods was 73%, mainly due to samples that tested negative by culture but positive using the molecular approach (54% of the total positive samples). The cases positive by SF alone were mostly samples from patients with initial concordant results on samples harvested before the administration of a specific antimicrobial therapy, or, importantly, sample positive for a clinically relevant agent such as Aspergillus fumigatus, which is hard to detect by the traditional approaches.

The LightCycler SeptiFast test gives new insights into the natural history of infection and in the development of new algorithms for the diagnosis of sepsis in critical patients. Using SF combined with BC improves microbiological documentation in febrile neutropenia particularly in persistent fever despite antibacterial therapy, when a nonresponding bacterial infection or an invasive fungal infection is suspected; results of SF may lead to a more targeted antibiotic therapy early after the onset of fever.

No relevant conflicts of interest to declare.