Researchers from the University of Nebraska Medical Center conducted a trial to measure if using a specific device for blood collection would reduce the rate of culture contamination.
University of Nebraska Medical Center (UNMC) researchers recently conducted a single center, prospective, controlled trial to establish whether the use of a Steripath initial specimen diversion device (ISDD) decreased contamination of blood cultures in emergency department patients.
According to the study, blood cultures are usually collected to test for bacterial and fungal infections, as well as to “guide specific antimicrobial therapy.” Rates of blood culture contamination can range anywhere between 0.6% and 6% contamination in US healthcare facilities. It is believed that blood cultures become contaminated when skin fragments contaminated with bacteria are “dislodged with venipuncture,” according to the authors. This contamination can result in additional laboratory and treatment expenses; more specifically, tests that yield false-positives, potentially due to this contamination, can result in around 20% increase in lab charges, as well as about a 40% increase in antibiotic costs, due to unnecessary prescribing. Furthermore, a patient can spend up to 5 additional days in the hospital, experience toxicity, drug interactions, and negative side effects, all from false blood culture results. According to a press release on the study, false cultures subsequently “contributes to antibiotic resistance and undermines nationwide efforts to improve antimicrobial stewardship.”
Because the authors hypothesized that contamination occurs as a result of contaminated skin fragments mixing with the sample during venipuncture, the authors set out to “test a device that diverts and sequesters the first 1.5—2 mL portion of blood, which presumably carries the contaminating skin fragments, from the culture specimen to determine whether blood culture contamination is diminished.”
The study included 2 blood cultures collected from each of 904 patients who “require[ed] phlebotomy for blood culture due to clinical suspicion of serious infection.” The majority of the study subjects were male (55%), with an average age of 59 years.
Samples were collected between November 2014 and October 2015. The authors compared standard blood culture collection procedures with that of the Steripath ISDD. Patient skin was disinfected with 2% chlorhexidine gluconate and 70% alcohol for 30 seconds and left to dry before samples were collected. The culture vials were properly disinfected using “70% isopropyl alcohol pads before inoculation.” The first sample from each patient was acquired through a syringe and inserted into a blood culture vial—standard blood culture collection procedures. For the second sample, after the syringe was inserted, the Steripath ISDD separated the first 1.5-2.0 mL of blood into a “holding chamber” and directed the remainder of the blood into the collection vial.
According to the study parameters, a blood culture sample was found to be contaminated if coagulase-negative staphylococci, Propionibacterium sp., Micrococcus sp., viridians group streptococci, Corynebacterium sp., or Bacillus sp. was identified in one of the cultures. The researchers found that the “most common cause of true bacteremia were the Enterobacteriaceae (39%) followed by [Staphylococcus] aureus (20.7%).” Sixteen samples collected through the standard procedure showed contamination. More than half of these were caused by coagulase-negative staphylococci (51%), followed by Propionibacterium sp. (19%). On the other hand, 2 samples collected through the Steripath ISDD procedure showed contamination.
The authors wrote, “Discordance between the 2 methods of phlebotomy with regard to detection of true bacteremia was essentially equal. In 12 instances, the standard procedure yielded a true pathogen while the ISDD was sterile, and in 11 instances, the ISDD yielded a true pathogen while the standard procedure was sterile.” According to the authors, these findings stress the need for 2 blood cultures in order to effectively identify true bacteremia; the incidence of detecting of true bacteremia with a single blood culture was 73%.
The authors concluded that use of the Steripath ISDD significantly decreased the number of false positive results. Contamination rates went down from 1.78% to 0.2%, which was observed to be an 88% reduction.
In comparing the number of contaminated blood cultures obtained 6 months before and 6 months after the study, the authors noted that the use of both blood culture collection procedures resulted in the prevention of 373 contaminations. They write, “The costs associated with blood culture contamination range from $1000 (1998) to $8700 (2009) per case. If a midpoint cost estimate is used ($4850), and the added cost of the device is not taken into account, it equates to a cost avoidance of $1.8 million per year at our institution.”
Commenting on the study’s findings in a press release, Mark Rupp, MD, professor and chief of the UNMC Division of Infectious Diseases and medical director of the Department of Infection Control and Epidemiology at Nebraska Medicine said, “The 1.78% baseline rate of contamination may seem small, but we should strive to decrease adverse events to the lowest possible level because of the impact to the patient and the burden to our healthcare system. We quite clearly showed the rate of contamination was significantly reduced, and that decrease has a very big impact.”