Blood cultures - how many sets? how many bottles?

So until last week I thought all microbiologists agreed that we should aspire to 2 sets of blood cultures. I now discover that some people not only think that 2 sets is overkill, they also are happy with just one bottle! There seems some doubt as to whether this should be the aerobic or anaerobic. Anyway, made me look at our data. I’m sure others have done likewise. Be interesting to combine experiences…

 Effect of multiple sets on positivity rate (significant growth only)

 So we now get 2 sets of blood cultures sent from the ED in about 20% of cases. And the second set does not add a huge amount of value.

 90% of positive episodes in which 2 sets were taken were positive in both sets

 Taking a second set of cultures probably increases coliform detection by about 5-10%

 There was little effect on isolation of other significant organisms
Bottle type and positivity

 Looking at all significant culture results, which bottles were positive?

 674 / 1053 significant blood cultures were detected in both bottles

 217 / 1053 were detected in anaerobic only

 162 / 1053 were detected in aerobic only

Conclusions

 Taking more than 1 set may not add much value. But not taking an aerobic and anaerobic bottle - I find it harder to understand that. You will miss important pathogens quite frequently. I would be happy to promote properly filled single sets (aerobic and anaerobic).

 Another metric we could maybe get out of the newer blood culture machines is around bottle fill volumes. Perhaps another thing to base quality improvement around? But if anyone has similar data then perhaps we should combine and make a paper out of this. Particularly given the

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