Nucleic acid amplification-based pathogen detection in the blood of severe sepsis patients

Background

Blood culture is an important method for identifying the underlying microorganism causative of sepsis. However, appropriate antibiotic therapy may possibly be delayed due to the long time to results for culture-based methods. Nucleic acid amplification (NAT) of microbial DNA may significantly shorten the time to pathogen detection but clinical data for this technique are missing. The goal of the present study was to compare a new NAT protocol with blood culture results in critically ill patients with evidence of infection.

Methods

Patients either with severe sepsis (sepsis group) or systemic inflammatory response syndrome without evidence of infection (control group) were included. A blood culture (BC) was obtained and 10 ml ethylenediamine tetraacetic acid blood was simultaneously taken by sterile venous puncture. Microbial DNA was measured using NAT-based pathogen detection with multiplex PCR testing for 45 targets (VYOO^®; SIRS-Lab, Jena, Germany).

Results

Thirty-six samples from 24 septic patients (age 66.0 ± 3.4 years) and 32 samples from 22 control patients (age 64.6 ± 5.1 years) were obtained. The PCRs of all control patients were negative while five BCs from the control group (15.6%, P = 0.06) were positive. In sepsis patients, five BCs (13.4%) tested positive compared with 14 positive PCRs (38.9%, P = 0.03). Median procalcitonin levels were higher in PCR-positive tested sepsis patients (7.0 ng/ml; interquartile range, 1.5 to 14.5) compared with patients with negative PCR (1.8 ng/ml; interquartile range, 1.0 to 6.2). However, the difference did not reach statistical significance (P = 0.15). No similar correlation between procalcitonin and findings of BC were observed. Procalcitonin for negative BCs was 2.4 ng/ml (1.4 to 7.6), and was 2.1 ng/ml (0.4 to 9.2, P = 0.35) for positive BCs.

Conclusion

Multiplex PCR detected pathogens significantly more often than the concomitant BC, while there was no rate of false positive results in patients without evidence of infection. Positive PCRs were associated with higher serum procalcitonin levels, thus suggesting the clinical importance of a positive PCR result. Larger sample sizes are needed to confirm these observations.