Background
Methods
Sites
Blood cultures
Storage condition | Per organism | Total | ||||
---|---|---|---|---|---|---|
COMRUa | LOMWRUa | SMRUb | LOMWRUb | Total | ||
No storage | ×5 | ×5 | × 5 | ×3 | ×18 | 90 |
6 h 25 °C | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
6 h cool-box | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
6 h 40 °C | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
12 h 25 °C | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
12 h cool-box | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
12 h 40 °C | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
24 h 25 °C | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
24 h cool-box | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
24 h 40 °C | × 5 | × 5 | × 5 | × 3 | × 18 | 90 |
Total | 50 | 50 | 50 | 30 | 180 | 900 |
Statistical analysis
Results
Inoculum
Sub-culture results
Positive blood culture yield
Time (h) | Temp (°C) | Bottles (n) | Positive (n)a | Positive (%) | P valuec | Sensor positived |
---|---|---|---|---|---|---|
0 | NA | 90 | 80 | 88.9 | NA | 0/25 |
6 | 25 °C | 90 | 85 | 94.4 | 0.281 | 0/25 |
6 | Cool-box | 90 | 81 | 90.0 | 1.000 | 0/25 |
6 | 40 °C | 90 | 74 | 82.2 | 0.289 | 0/25 |
12 | 25 °C | 90 | 76 | 84.4 | 0.511 | 0/25 |
12 | Cool-box | 89b | 80 | 89.9 | 1.000 | 0/25 |
12 | 40 °C | 90 | 77 | 85.6 | 0.656 | 15/25 |
24 | 25 °C | 90 | 82 | 91.1 | 0.805 | 20/25 |
24 | Cool-box | 90 | 71 | 78.9 | 0.104 | 20/25 |
24 | 40 °C | 90 | 59 | 65.6 | < 0.001 | 20/25 |
6 | All | 270 | 240 | 88.9 | 1.000 | 0/75 |
12 | All | 269b | 233 | 86.6 | 0.787 | 15/75 |
24 | All | 270 | 212 | 78.5 | 0.030 | 60/75 |
All | 25 °C | 270 | 243 | 90.0 | 0.841 | 20/75 |
All | Cool-box | 269b | 232 | 86.2 | 0.694 | 20/75 |
All | 40 °C | 270 | 210 | 77.8 | 0.021 | 35/75 |
Time to positivity
Visual detection of growth
Discussion
S. pneumoniae autolysis
Impact of delayed incubation on yield
Impact of delayed incubation on time to positivity
Visual detection of growth
Utility of blind sub-cultures
Automated versus manual blood cultures
Study design and limitations
Conclusions
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BC storage time should be minimized where possible (preferably no longer than 12 h);
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if storage for longer than 12 h is unavoidable, BC bottles should be protected from high temperatures, for example by storing them in a cool-box (maintaining a temperature of approximately 25 °C was shown to be suitable in this study) away from direct sunlight;
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a blind sub-culture prior to incubation on all BC bottles that have had prolonged storage should be performed (preferably on all bottles that have been stored for ≥ 12 h);
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for manual BC systems, visual inspection alone should not be relied upon and at least one sub-culture following 24 h incubation should be performed; and
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for automated BC systems, delays in sub-culturing bottles that have flagged positive should be minimized (this and a previous study support a maximum delay of 7 h to maximize the recovery of S. pneumoniae).