Comparison of Real-time PCR method and blood culture in diagnosis of septicemia

Author(s): Bloodstream infections (BSI) have a high incidence and high mortality in the worldwide. The mortality rate is variable between 20-70%. Therefore, early and timely detection of BSI agent in clinical laboratories is necessary. The aim of this study was to determine an efficient diagnostic tool to septicemia in accompany of blood culture method by Real-time PCR (using panbacterial 23S rRNA gene).
This cross-sectional study was conducted in two analytical and clinical stages in Hamadan University of Medical Sciences, Iran, from October 2014 to June 2015. In analytical stage, sensitivity (by serial dilution from 104 to 1 CFU/ml) and specificity of the primer were evaluated with the Staphylococcus aureus (as Gram positive indicator bacteria) and Escherichia coli (as Gram-negative indicator bacteria), human genome (from Hella cell culture), Candida albicans yeast and Aspergillus fumigatus fungus. In clinical stage, 121 blood samples were collected from patients suspected to sepsis in intensive care unit (ICU) from Hamadan University Hospitals. Finally, the results of Real-time PCR and blood culture methods were compared.
The Real-time PCR showed a sensitivity ranging from 2 to 10 target copies per reaction to the whole blood for Escherichia coli and Staphylococcus aureus respectively. The specificity of this method was evaluated and no false positive amplification was identified. 57.85% (70 cases) of the samples were positive by Real-time PCR and 13.22% (16 cases) of the samples were positive by blood culture. However, none of the cases that were positive by blood culture were negative in Real-time PCR. As well as, 44.62% (54 cases) of cases were positive by Real-time PCR but blood culture showed no bacteria in the samples, and 42.15% (51 cases) were negative by both methods. Correlation or agreement of Kappa was 0.20, that indicating poor agreement between the two methods.
Real-time PCR is more sensitive than blood culture and also, because of high sensitivity of this primer by Real-time PCR, we can use it for screening blood samples from suspected patients of sepsis.