Comparative evaluation of Oxoid Signal and BACTEC radiometric blood culture systems for the detection of bacteremia and fungemia

Abstract

The Oxoid Signal (Oxoid U.S.A., Inc., Columbia, Md.) blood culture system is a newly described, innovative method for visually detecting growth of microorganisms (D. Sawney, S. Hinder, D. Swaine, and E. Y. Bridson, J. Clin. Pathol. 39:1259-1263, 1986). We did 5,999 paired comparisons of equal volumes (10ml) of blood in the Oxoid Signal and BACTEC (Johnston Laboratories, Towson, Md.) radiometric blood culture systems at two university hospitals that use identical methods of obtaining and processing specimens. Overall, more microorganisms were detected in the BACTEC system(P < 0.001), in particular, streptococci (P < 0.01), fungi (P < 0.001), and nonfermentative gram-negative rods, especially Acinetobacter species (P < 0.001). Trends favoring the BACTEC system for detection of Pseudomonas aeruginosa, Haemophilus species, and Neisseria species were noted. There were no differences in the yield of staphylococci, members of the family Enterobacteriaceae, and anaerobic bacteria. When both systems detected sepsis, the BACTEC did so earlier (P < 0.001). This advantage was most notable at 24 h (70% of BACTEC positives detected versus 48% of Oxoid positives). The proportion of positives detected after 48 h, however, was similar (BACTEC, 84%; Oxoid, 78%). Revisions in the Oxoid Signal system itself or in the processing of Oxoid bottles appear to be necessary to improve its performance in detecting certain microorganism groups, especially fungi.