Blood Culture Contamination: A Cluster‐Randomized Crossover Trial Evaluating the Comparative Effectiveness of 3 Skin Antiseptic Interventions

Background:

Blood cultures are one of the most commonly performed and valuable diagnostic procedures in hospitalized patients. Contaminated blood cultures, however, result in significant resource utilization and potential complications from exposure to unnecessary therapies. Various antiseptic agents have been studied in clinical settings, but there is no consensus in the literature regarding which agent is superior in reducing blood culture contamination. Currently, the 3 most routinely employed skin antiseptics are 10% povidone‐iodine (PI), 2% iodine tincture (IT), and 2% chlorhexidine gluconate (CHG), with a substantial cost difference among them (PI $0.19, IT $0.59, and CHG $1.22). We sought to determine the relative rates of contaminated peripheral blood cultures when the 3 skin antiseptic agents (PI, IT and CHG) were used by a dedicated phiebotomy team in adult non‐ICU medical and surgical patients.

Methods:

We employed a randomized cluster design using hospital floor as the unit of randomization, skin antiseptic as the intervention variable, and rate of contaminated blood cultures as the primary outcome. Each antisepsis intervention was used for 5 months on 3 separate floors, with the sequence differing between floors in a crossover design. Dedicated phlebotomy teams collected all peripheral blood cultures using a standard protocol with skin antisepsis varying according to study design. Random auditing was performed to ensure compliance with the intervention. Blood cultures were processed by the hospital microbiology lab according to standard protocols. Each positive blood culture was evaluated by 2 attending infectious diseases (ID) physicians blinded to the intervention and scored as true positive or contaminated using standardized definitions. A third attending ID physician evaluated discordant results.

Results:

A total of 12,968 peripheral blood culture sets were evaluated over a 15‐month period, of which 740 (5.7%) were positive. There were 101 contaminated cultures representing 13.6% of all positive cultures. Predominant organisms in contaminated cultures were coagulase‐negative staphylococcus (76.2%), micrococcus (8.9%). and bacillus species (6.9%). The intention‐to‐treat rates of contaminated blood cultures were similar among the 3 antiseptics (P = 0.22); 0.60% with PI (95% Cl, 0.39%–0.8S%), 0.80% with IT (95% Cl, 0.55%–1.11%), and 0.93% with CHG (95% Cl, 0.67%–1.26%). There was a significant difference in positive predictive value for a true‐positive blood culture among the 3 antiseptics (91.7% for PI 85.2% for IT, and 82.3% for CHG; P = 0.017).

Conclusions:

The rate of contaminated blood cultures was not significantly affected by the choice of antiseptic agent when peripheral blood cultures were obtained by a dedicated phlebotomy team. The probability of having a true‐positive blood culture, however, was highest with PI. Given the greater predictive value of true‐positive blood culture and the lower acquisition cost, PI may be the current antiseptic agent of choice.

Author Disclosure:

H.‐W. Kim, none; L. Washer, none; C. Chenoweth, none; A. Malani, none; J. RidelI, Pfizer and Merck, grants; L. Kuhn, none; M. Rogers, none; H. Neusius, none; S. Saint, none; S. Flanders, none.