Initial detection of bacteremia by subculture of unvented tryptic soy broth blood culture bottles.

Routine subculture of macroscopically negative blood cultures is a traditional blood culture procedure. The need to perform routine early (6-17 hr) and late (48 hr) subculture of unvented blood culture bottles when a simultaneous subculture of the vented bottle is performed has been questioned. Blood cultures in paired vented and unvented tryptic soy broth (TSB) bottles from 4574 patients were examined retrospectively. Subculture of unvented TSB bottles provided initial detection of 412 (5.0%) isolates from 277 (6.1%) patients and was comparable to that of vented TSB bottles for Pseudomonas and all other microorganisms, except for the Enterobacteriaceae (p less than 0.001; vented TSB), Candida (p less than 0.001; vented TSB), and Haemophilus influenzae (p less than 0.01; unvented TSB). Of the H. influenzae isolates, 46% were detected initially by subculture of the unvented TSB bottles; early subculture recovered 67% of these isolates. The value of subculture of unvented TSB bottles is minimized when subculture of the vented TSB bottle is routinely performed; however, routine subculture of the unvented bottle is recommended whenever TSB is used for detection of bacteremia in patients in whom H. influenzae infection is possible.