Determination of the optimum incubation period of blood culture broths for the detection of clinically significant septicemia.

The value of incubating blood culture broths for more than 7 days was analyzed. A total of 20,155 blood cultures, consisting of a vented Roche tryptic soy broth (R-TSB) bottle and an unvented Difco thiol broth bottle, was processed; 2,509 organisms were recovered in the R-TSB bottles, and 1,865 organisms in the thiol bottles. Only 32 organisms isolated in the R-TSB bottles and 10 organisms isolated in the thiol bottles were detected after incubation for more than 7 days; 15 of the 32 isolates in the R-TSB bottles and all 10 of the isolates in the thiol bottles were either recovered in other blood cultures or were not considered to be clinically significant. Thus, incubation of the R-TSB bottles and unvented thiol bottles for more than 7 days is unnecessary for the detection of most clinically significant septicemias.