Blood cultures are indicated if the patient displays systemic signs of infection or has pyrexia of unknown origin, and should be taken when the patient’s temperature spikes, as the numbers of bacteria circulating within the bloodstream will be at their greatest then. 20–30 mL of blood is drawn which is inoculated into separate culture bottles containing liquid culture media, one for aerobic and one for anaerobic incubation, and it should be transported to the laboratory immediately.
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Box 6.5 Protocol for undertaking MRSA screens (nose and axillae): broth method
2 × plastic tipped swabs (supplied with the broth) 1 × broth (Note: 1 broth bottle per patient screen) 1 × printed label (patient details)
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Hands must be decontaminated prior to undertaking the procedure (gloves are not strictly necessary, but non-sterile examination gloves may be worn).•
Swab both nostrils with 1 x plastic-tipped swab.•
Open the broth bottle and swirl the plastic-tipped swab in the broth for 5 seconds.•
Discard the swab as clinical waste; replace the lid on the broth.•
Swab both axillae with 1 x plastic-tipped swab.•
Open the broth bottle and swirl the plastic-tipped swab in the broth for 5 seconds.•
Discard the swab as clinical waste; replace lid on the broth.•
Decontaminate hands.•
Fix printed label to the broth bottle; complete and print the Specimen Request Form.Fact Box 6.4 Blood culture collection
Blood culture collection is a skilled procedure and must be undertaken only by Nurses, Phle- botomists and Medical Staff who have received training and passed a competency assessment (this should be undertaken annually and form part of mandatory training). If the skin is not decontaminated appropriately prior to drawing the blood, the culture may become contami- nated with skin flora such as coagulase-negative staphylococci (Marwick et al., 2006; Murray and Witebsky, 2010). The isolation of MRSA from a blood culture is not necessarily clinically significant if the patient is systemically well, and may indicate contamination as opposed to clinical infection. However, contaminated blood cultures will be reported as avoidable.
Contaminated blood cultures are by and large preventable through sound aseptic technique and optimal skin decontamination (Department of Health [DH], 2007; Rowley and Clare, 2011).
The DH (2007) published Taking Blood Cultures: Summary of Best Practice as guidance for NHS Trusts in order that they could effectively review their policies and practices and reduce the risk of, and number of, contaminated cultures. Box 6.6 lists the indications for blood culture collection, and Box 6.7 lists the best practice for the prevention of contaminated blood cultures.
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Box 6.6 Indications for blood culture collection
Core temperature out of normal range (>38oC) Focal signs of infection
Other signs of septic shock, such as acute circulatory failure, low blood pressure and/or increased respiratory rate
Chills and/or rigors within the previous 24 hours Raised or very low white cell count
New or worsening confusion Data from DH, 2007.
Box 6.7 Best practice: prevention of contaminated blood cultures
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Only staff who have been assessed as competent in blood culture collection should be permitted to undertake the procedure (mandatory annual training and competency assessment).•
Use a dedicated blood culture collection pack.•
If blood is being collected for other tests, collect the blood culture first.•
Do not use existing cannulae or sites immediately above existing cannulae. If a central venous catheter (CVC) is in situ, blood can be taken from the CVC but the hub must be disinfected using a 2% chlorhexidine in 70% alcohol swab, and blood must be taken from a separate peripheral venous stab first.•
Never take a blood culture from a femoral stab due to the high risk of contamination. Blood may be taken from a newly sited cannula after disinfecting the hub with a 2% chlorhexidine in 70% alcohol swab as long as the skin was decontaminated with 2% chlorhexidine in 70%alcohol prior to the cannula being inserted.
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Decontaminate hands prior to decontaminating the patient’s skin, prior to putting on examination gloves (which should be just before attaching the winged blood culture collection set to the blood collection adaptor cap), and after removing gloves (once the winged blood collection set has been discarded into the sharps container).•
Use 2% chlorhexidine in 70% alcohol to decontaminate the patient’s skin, and allow to dry;do not re-palpate the skin.
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Always make a fresh stab in patients with suspected bacteraemia (it is recommended that two sets of cultures are taken at different times from different sites).93
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Use a 2% chlorhexidine gluconate in 70% alcohol swab to decontaminate the blood culture bottle tops (these are clean but not sterile), and allow to dry (approximately 30 seconds) before inoculating the bottles.•
Document the procedure in the patient’s notes – indication for blood culture; date and time; site of blood culture; signature and print name; and bleep and telephone number.Note: Completion of a pre-printed ‘Record of Blood Culture Collection Label,’ containing the above information and a statement that the blood culture has been collected according to Trust policy by a healthcare worker who is competent to undertake the procedure, helps to provide assurance that best practice has been followed. In the event of the patient being found to have an MRSA bacteraemia, the person who took the blood culture should be contacted by the Infection Prevention and Control Team and asked to (1) describe step by step the procedure that he or she used and (2) provide evidence that he or she has completed the appropriate training and passed the competency assessment.
Source: Data from DH, 2007.