Fast Facts

Over the past 30 years, strategies to decrease blood culture contamination rates in US hospitals have included the use of specific disinfection materials, educational interventions, collection from separate venipuncture sites, a double-needle technique, employing a discard tube, and reliance on specially-trained staff or dedicated phlebotomists. But, because widespread and sustainable reductions have been illusive, hospitals have come to accept a 3% contamination rate as the standard of care.

Read the highlights from published clinical studies to better understand the incidence of contamination that leads to false positive blood cultures, the associated costs of contamination, and the on-going measures to reduce contaminated blood cultures.

Incidence

Standards published by the American Society for Microbiology state that acceptable contamination rates should be no higher than 2 to 3%.
(Dunne, WM et al. ASM Press, Washington, DC. 1997.)

Estimated up to 50% of all blood cultures originate in ED. Increasing crowding in EDs is correlated with higher rates.
(Garcia RA et al. AJIC. 2015)

Contaminated blood culture rates vary widely from 0.6% to over 6% and rates have been on the increase.
(Hall and Lyman. Clin Microbiol Rev. 2006)

Contamination rates among individual clinicians range widely (0% to 21%)
(Murillo TA. Pediatr Emerg Care. 2011)

Previous studies have demonstrated that blood culture contamination rates are usually higher at teaching hospitals, sometimes exceeding 7%.
(Schifman RB et.al. Arch. Pathol. Lab. Med. 1998.)

Costs

There is an increased length of stay of 3.2 days associated with false positive blood cultures.
(Allain M. Clin Nurs Specialist 2018)

False positives increase laboratory costs by approximately 20%, are associated with a nearly 40% increase in antibiotic charges and can extend the length of hospital stay by up to 5 days.
(Rupp MS et al. Clin Infect Dis. 2017.)

Charges for a patient with a false-positive in 2009 were $8,720 more than charges for a patient with a negative blood culture results.
(Gander RM et al. J Clin Microbiol. 2009)

About 60% report that hospitals likely submit CLABSI data to NHSN attributable to blood culture contamination, needlessly exposing the hospital to reduced funding.
(Garcia RA. Am J Infect Control. 2017)

Although only 6% of the blood cultures represented contaminants, their associated cost was more than twice that associated with the 87% that were true negatives.
(Zwang O, et al. J Hosp Med. 2006)

The percent increase in patient charges associated with contaminated blood cultures is approximately 50%.
(Bates DW. Et al. JAMA 1991.)

A 50% reduction in false positives would save approximately twice as much as a 50% reduction in false negatives.
(Zwang O, et al. J Hosp Med. 2006)

False positives increase laboratory costs by approximately 20%.
(Gander RM et al. J Clin Microbiol. 2009)

False positives increase the need for additional cultures and other tests.
(Norberg A. JAMA. 2003.)

False positives are treated with antimicrobials up to one half of the time and associated with a nearly 40% increase in antibiotic charges.
(Madeo M et al. 2005. Emerg. Med. J. 22:810-811.)

False positives increase the workload of technologists and other staff.
(Schifman RB. Arch. Pathol. Lab. Med. 1998.)

Prevention

Skin, however, cannot be sterilized during antisepsis procedures because approximately 20% of bacteria are imbedded within deep layers of the epidermis and dermis.
(Garcia RA. Am J Infect Control. 2015)

Respondents in a national survey reported that 90% of hospital protocols emphasize direct venipuncture.
(Garcia RA. Am J Infect Control. 2017)

About half of blood culture contamination results are shared with the unit where it was collected.
(Garcia RA. Am J Infect Control. 2017)

More than 96% of bacteremias are detected with two or three blood culture sets.
(Cockerill FR et al. Clin. Infect. Dis. 2004.)

Direct venipuncture results in fewer contaminated blood cultures.
(Snyder SR. Clin Biochem. 2012)

False positive blood culture rates among phlebotomists (3.1) are lower than among non-phlebotomists (5.6 – 7.4).
(Gander RM et al. J Clin Microbiol. 2009)

The rates of contaminated blood cultures among the various antiseptic agents used to prepare the venipuncture site are not statistically different.
(Story-Roller E, et al. J Clin Microbiol. 2016) (Washer LL, et al. Infect Control Hosp Epidemiol. 2013)

Venipuncture needles soil blood culture specimens with unsterilized skin fragments and increase blood culture contamination rate. Initial specimen diversion technology significantly reduces the rates from venipuncture-obtained blood culture specimens.
(Patton RG, Schmitt T. J Clin Microbiol. 2010)

Only 6% of respondents in a national survey said they discard the initial aliquot of blood prior to inoculating the blood culture bottle for peripheral draws and 54% did for central draws.
(Garcia RA. Am J Infect Control. 2017)

Diversion is credited with having reduced contamination of blood components by 40 to 90% between 1995 and 2007.
(Liumbruno GM, Blood Transfus. 2009)

Reductions in contamination of blood cultures may be realized with diversion volume <1ml, as a 21-gauge culture needle (bore, 0.514 mm) captures a minute plug of skin contaminants.
(Patton RG, Schmitt T. J Clin Microbiol. 2010)

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