Improving the performance of culture-based bacterial screening by increasing the sample volume from 4 mL to 8 mL in aerobic culture bottles.
BACKGROUND
In the setting of bacterial detection of apheresis platelets (PLTs), the manufacturer recommended PLT inoculation volume for BacT/ALERT culture bottles (bioMérieux) ranges from 4 to 10 mL. This study compares the rate of capture of true-positive (TP) contaminations between aerobic culture bottles inoculated with either 4 or 8 mL of sample and assesses if a larger sample volume reduces time to detection.


METHODS
Detection of TP samples and mean time to detection were compared for 4- and 8-mL samples collected between September 1, 2003, and May 2, 2011.


RESULTS
A total of 180,263 and 283,114 PLT collections were tested with an 8- and 4-mL sample, respectively. Analysis of TP rates by volume sampled show an increase in the rate of detection of TP with the 8-mL sample relative to the 4-mL sample (139 vs. 106 per million events; odds ratio, 1.31; 95% confidence interval, 0.77-2.23). Comparison of mean time to detection for TP shows a decrease in mean time to detection using 8 mL compared with 4 mL (12.36 ± 3.7 hr to 15.97 ± 6.3 hr, p = 0.012).


CONCLUSIONS
Doubling the sample volume to 8 mL showed a trend in improvement for the rate of detection of TP and shortened the mean time of detection for TP by 23% when compared to a sample volume of 4 mL. The decrease in mean time to detection using a larger sample volume suggests that a shorter release time after inoculation could be achieved without significantly increasing patient risk.
United Blood Services Arizona, Scottsdale, AZ, USA.
Stephanie
S
Souza
Marjorie
M
Bravo
Terri
T
Poulin
Sandra
S
Vanderpool
Hany
H
Kamel
Peter
P
Tomasulo
Leon L
LL
Su
D000332:Aerobiosis; D001419:Bacteria / Q000254:growth & development / Q000302:isolation & purification; D001424:Bacterial Infections / Q000517:prevention & control / Q000635:transmission; D001431:Bacteriological Techniques / Q000295:instrumentation / Q000379:methods; D001792:Blood Platelets / Q000382:microbiology*; D006801:Humans; D012680:Sensitivity and Specificity; D013997:Time Factors