Evaluation of blood culture procedures in a pediatric hospital

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Abstract
To determine optimal clinical laboratory techniques for detecting pediatric bacteremia, 7768 consecutive blood cultures were studied in 1 yr. Blood was inoculated into 1 vented 50 ml bottle of Brucella broth with 0.05% sodium polyanethosulfonate and 1 unvented 50 ml bottle of Columbia broth with 0.05% sodium polyanetholsulfonate and 0.05% cysteine. Bottles were visually examined for growth on days 1-7 and blindly subcultured aerobically and anaerobically on days 1, 2 and 7. There were 724 (9.3%) positive cultures and 484 (6.2%) were clinically significant. The most frequent isolates from bacteremic patients were Haemophilus influenzae (24%) and Streptococcus pneumoniae (17%). Growth was noted in only 1 bottle in 25% of clinically significant isolates. Bottles inoculated with .gtoreq. 1 ml of blood became positive earlier than bottles inoculated with < 1 ml. After 1 day of incubation, 48% of the clinically significant cultures showed growth on visual examination; 85% showed growth on subculture. Of Haemophilus isolates, 19% were detected visually on day 1 and 88% were recovered on subculture. By day 7, 3.5% of all isolates (including 18% of pneumococcal isolates and 1% of Haemophilus isolates) could no longer be recovered on subculture. A 2 bottle blood culture system and blind subculture within 24 h optimizes detection of pediatric bacteremia.