We analysed the clinical utility of the standardised, Conformite Europeanne-certified, multiplex real-time PCR assay for the molecular diagnostics of sepsis that was approved for in vitro diagnostics use (LightCycler SeptiFast assay; Roche Diagnostics, Pleasanton, CA, USA). The SeptiFast assay enables detection of DNA from 25 human pathogens (Gram-positive and Gram-negative bacteria as well as fungi).
The study enrolled 50 patients with clinical diagnosis of sepsis that received medical care at the University Hospital for Infectious Diseases, Zagreb and Zagreb University Clinical Center in Croatia. Ten patients were treated at the Department of Haematology following bone marrow or peripheral blood stem cell transplantation; 30 patients were hospitalised in the ICU and 10 patients outside the ICU. All patients enrolled in the study were already receiving empirical antimicrobial therapy at the time of testing.
Peripheral blood samples from the patients were analysed using the LightCycler SeptiFast assay and cultivation.
Fifteen out of 50 (30%) samples tested positive with the SeptiFast assay for bacterial or fungal DNA. Gram-negative bacteria were detected in 13 of 15 samples (Klebsiella pneumoniae/oxitoca, n = 6; Escherichia coli, n = 3; Pseudomonas aeruginosa, n = 4). Gram-positive bacterial DNA (Enterococcus faecium, n = 1 and Streptococcus pneumoniae, n = 1) was detected in two patients with polymicrobial sepsis (in combination with K. pneumoniae/oxitoca in both patients). Aspergillus fumigatus DNA was detected in two patients. Six out of 50 samples (12%) were positive by both SeptiFast assay and culture. Additional SeptiFast-positive results (negative by cultivation) were obtained in nine of 50 patients (18%). Four out of 50 samples (12%) tested negative by the SeptiFast assay but were positive by culture. Those results were interpreted as false negative molecular testing. The remaining 31 samples tested negative by both SeptiFast assay and culture. In the group of 10 haematological patients, SeptiFast results were positive for six of the 10 patients (60%), whereas blood cultures were positive in only two out of 10 patients (20%).
We conclude that the SeptiFast assay is a clinically valuable add-on to conventional culture methods for rapid aetiological diagnosis of sepsis in patients where the empirical antimicrobial therapy has already been started and pretreatment blood cultures were negative.