HAEMATOLOGY
Burden of blood culture contamination
False positive blood cultures lead to unnecessary treatment and prolonged hospital stays. Étáin O’Keefe RGN and Stuart Murray discuss the importance of preventing the clinical and economic burden of blood culture contamination.
Blood culture is considered to be the ‘gold standard’ method of investigation for the detection of microorganisms in the blood that lead to the diagnosis of serious infections. However, blood cultures continue to be a source of frustration to clinicians and microbiologists and a burden to healthcare systems due to erroneous results caused by contaminated samples.
The universally ‘acceptable’ blood culture contamination (BCC) rate is currently quoted as 3%.1
Although with many papers
discussing different methods of reducing BCC rates and with new technology coming to the market there is now an argument that for such an important diagnostic tool, this rate should be significantly lower.1
of a microorganism during the collection phase of the sample.1
Tests can become
contaminated from several sources such as the patient’s skin, the equipment used to take the sample, the hands of the person taking the blood sample, or the environment. Emergency departments are regularly identified as the main source of high contamination rates within hospitals.1, 3, 4 This may be due to high staff turnover rates, high numbers of blood cultures taken in emergency departments, fast paced nature of the environment or taking cultures from a venous access device that may have already been used and thus contaminated.1
BCC can Studies from both North
America and Europe illustrate widely varying contamination rates between institutions, from as little as 0.6% to over 10%.2 In UK & Irish hospitals BCC is reported on average as 5% false positive rate. With 3.5M blood cultures performed annually results in approximately 175,000 false positive blood cultures a year. This creates an enormous burden within an already stretched clinical environment and heightens the need for diagnostic testing to be accurate and reliable.
What is a blood culture contamination?
Blood culture contamination (BCC) usually occurs due to accidental cross contamination
When a sterile field is breached.
Preparation
Collection Set Assembly
From bacteria on clinicians hands or surfaces.
NOVEMBER 2020
also be caused by defective skin antisepsis or incompletely decolonised skin fragments becoming dislodged by venepuncture.5 Skin antisepsis using a sterile 2% chlorhexidine and 70% isopropyl alcohol applicator is evidenced as one of the best preventative measures for reducing contamination rates. However, more than 20% of the skin flora (microorganisms) may be beyond the reach of disinfection because microorganisms are located in pilosebaceous units (hair follicles, glands etc.)5
thus
meaning that, even with adequate education and aseptic procedure, there is a percentage of bacteria than cannot be sterilised and may become a source of contamination. It is widely reported today that nearly half of all positive blood cultures isolated are the
result of a contamination6 highlighting that
almost equal amounts of effort and resources are put into false positive samples and patient’s treatment as truly positive blood cultures.
Contamination creates clinical uncertainty
False positive results due to a contamination can prolong a hospital stay and trigger the administration of unnecessary antibiotics, placing patients at risk of complications from unneeded therapy, such as allergic reaction, and increased susceptibility to opportunistic infections like Clostridium difficile colitis.
and often results in detrimental downstream effects.7
These unintended consequences add significant additional healthcare costs, inconvenience for patients, occupy resources (hospital inpatient beds), delay treatment for others and increase length of stay in hospital.
Patient impact
Blood culture is a critical tool for healthcare staff, as it allows for both the identification and the subsequent targeting of specific microorganisms.3 However, contaminated samples producing incorrect results compromise the integrity of blood cultures as a diagnostic tool and place patients at risk of misinformed prognoses and incorrect targeted therapies. In cases where blood culture is used
When skin contaminants are drawn into the specimen.
Venepuncture
Sample Handing
When bacteria comes to reside on culture bottles.
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