Expansion
Two sets, separate sites, adequate volume, before antibiotics
Expansion
Technique
- Two sets from two separate venepuncture sites, each with an aerobic and anaerobic bottle
- 8 to 10 ml per bottle; yield rises roughly 3 per cent per additional millilitre
- Before antibiotics, but antibiotics must not be delayed in sepsis beyond the time it takes to draw them
- Aseptic technique with skin disinfection allowed to dry, and disinfection of the bottle tops
- Avoid drawing from existing lines unless investigating line infection, in which case take paired peripheral and line samples
- In suspected endocarditis, three sets from three sites, and in the subacute presentation they may be spaced over time
Interpretation
- Likely contaminant: coagulase negative staphylococci, Bacillus, Corynebacterium, Propionibacterium, growing in one bottle of one set with a long time to positivity
- Never a contaminant: Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli and other Enterobacterales, Pseudomonas, Candida. Each requires a source hunt and appropriate treatment
- Time to positivity under 12 hours suggests true bacteraemia and a high organism load
- Differential time to positivity, with the line sample positive at least 2 hours before the peripheral, suggests a line infection
Organisms that suggest a specific source
- Streptococcus gallolyticus (formerly bovis): colorectal carcinoma, so colonoscopy
- Streptococcus viridans: oral flora, endocarditis
- Clostridium septicum: colonic malignancy
- Candida: line, gut translocation, and it requires ophthalmology review and echocardiography
Staphylococcus aureus bacteraemia always warrants repeat cultures, an echocardiogram, a source search and a prolonged intravenous course; treating it as a contaminant is a recognised and serious error.