DELAYED INCUBATION OF BLOOD CULTURE BOTTLES - EFFECT ON RECOVERY RATEOF STREPTOCOCCUS-PNEUMONIAE AND HAEMOPHILUS-INFLUENZAE TYPE-B

This study investigated the effects of incubation delay on the rate of recovery of common pediatric pathogens from blood culture bottles. Kn own concentrations of Streptococcus pneumoniae and Haemophilus influen zae type b (three isolates each) were inoculated into BACTEC NR-6A(R) bottles with 1.0 mL of donor blood. Bottles were subjected to a time d elay (zero to six hours) before incubation. The BACTEC NR-660(R) was u sed for incubation and measurement of positive conversion. Data were a nalyzed using chi2 analysis, Fisher's exact test, logistic regression, and multiple logistic regression, with P < 0.05 considered significan t. Immediate incubation yielded positive blood cultures in 88 of 100 a nd 65 of 70 bottles containing S. pneumoniae and H. influenzae type b, respectively, in the concentration range 1.0 to 9.99 colony-forming u nits per milliliter (CFU/ml). For each organism, this was the minimal range required to produce a positive culture (P < 0.0001). Bottles ino culated with 1 ml of blood containing organisms in the range of 1.0 to 9.99 CFU/ml were then subjected to incubation delay. The recovery rat e of S. pneumoniae significantly (P = 0.0003) decreased from a two-hou r delay (57 of 60; 95%) to a three-hour delay (42 of 60; 70%). No sign ificant change in recovery rate was seen in bottles inoculated with H. influenzae type b subjected to similar delays. Delayed incubation (tw o to six hours) of bottles inoculated with 1.0 ml of blood containing organisms in a concentration range of 1.0 to 9.99 CFU/ml of blood sign ificantly decreases the recovery rate of S. pneumoniae but has no effe ct on H. influenzae type b.