Paired blood cultures increase the sensitivity for detecting pathogens in both inpatients and outpatients

The objective of this study was to show the differences between paired blood cultures (PBC) versus single blood cultures (SBC) in the microbiologic yield, the sensitivity to detect pathogens and the time to positivity (TTP). We performed a retrospective study examining 112,570 blood culture samples over a 5-year period from July 2011 to May 2016 in the BacT/ALERT® 3D automated blood culture system (bioMérieux, Marcy l'Etoile, France). Bacteria and yeasts were identified using the VITEK® 2 Compact system (bioMérieux, Marcy l'Etoile, France). True-positives and contaminated bottles were defined and analysed separately. We analysed TTP and adherence to blood volume guidelines for a convenience sample of 510 and 999 sequential positive cultures, respectively. Out of 49,438 PBC samples, 5810 (11.7%) were positive. In 63,132 SBC samples, 4552 (7.2%) were positive (p < 0.0001). In PBC, 5371 (10.9%) were true-positives and 439 (0.9%) contaminants. In SBC, 4095 (6.5%) were true-positives and 457 (0.7%) contaminants. In the inpatient departments (IPD), the most common isolate was Escherichia coli (n = 1373), followed by Klebsiella pneumoniae (n = 1206), whereas in the outpatient departments (OPD), the most common isolates were Salmonella typhi (n = 612) and S. paratyphi A (n = 278). In the analysis of TTP, 98% grew within 72 h, 91% within 48 h and 89% within 36 h. In the blood volume analysis, 90% of the cultures had optimal blood volume. A significantly higher positivity rate was seen in PBC compared with SBC. Our study adds to the increasing evidence of improved microbial yield of clinically significant bacteria and fungi by performing PBC instead of SBC and adhering to blood volume collection guidelines.