This single-center, retrospective observational study found that blood samples drawn from sites disinfected with ACHX exhibited a significantly lower proportion of contaminated blood cultures; this change was not apparently associated with a change in blood sampling technique. The most common source of infection among patients with true bacteremia was the urinary tract, and such patients typically presented with pyelonephritis. In contrast, the most prevalent source of infection among patients with contaminated and true negative blood cultures was pulmonary, with most such patients presenting with aspiration pneumonia, as judged by chart review and demonstrated by sputum culture and CT scan.
We also found that femoral sites were likely to be selected; selection of femoral artery for blood collection was significantly associated with contaminated blood cultures.
Several previous reports have described associations between topical disinfectants and blood culture contamination.18,19 A meta-analysis found that the rate of blood culture contamination is significantly decreased by disinfection with ACHX compared to that seen by disinfection with PVI.6 However, prior to our facility’s policy change, physicians at our hospital tended to disinfect puncture sites with PVI rather than with ACHX, for the following reasons. Firstly, physicians and ED staff were more familiar with PVI than ACHX because the former has been employed as a skin disinfectant for many years. Secondly, residents and medical students had not been educated about blood culture procedures while at university.
Our previous study revealed that femoral puncture sites comprise an independent risk factor for blood culture contamination.10 Physicians tend to collect blood from femoral arteries or veins because collection from this site is easier than collection from other sites. Femoral sites have been reported to be colonized more often than other sites,20 and these colonization events are associated with catheter-related bloodstream infection.21 However, the proportion of blood draws performed using femoral sites did not differ significantly between patients with and without contaminated blood cultures during the 2-year interval of the present study (Table 3). Thus, our regression discontinuity analysis indicated that the observed change in contamination rate was the result primarily of the change in disinfectants. Furthermore, this regression discontinuity analysis permitted determination of unbiased causal effect estimates, facilitating evaluation of intervention efficacy in a real-world circumstance.22,23
Pulmonary infection was the most-frequently found source of infection in patients with contaminated and true negative blood cultures. Pulmonary infection may cause pulmonary diseases such as pneumonia, bronchitis, pleuritis, and upper respiratory infection, without resulting in bacteremia. Several studies of patients with pulmonary disease have found that blood cultures provide little diagnostic benefit.24–26 However, other studies have indicated that blood samples should be cultured from select immunocompromised patients, from individuals with complicated UTIs who are under antibiotic therapy at the time of blood collection, and from patients with suspected endocarditis.25,27
Several strategies, including sampling from various venipuncture sites, reliance on a well-trained phlebotomy staff, and the informational intervention and feedback, have been advocated to reduce rates of blood culture contamination.5,28,29 Topical disinfection with olanexidine, which already is commercially available in Japan, also is expected to reduce the rate of blood culture contamination, given that this disinfectant recently was shown to exhibit stronger bactericidal activity than PVI for surgical site infection.30
This study has several limitations. First, our study was observational in design, and some physicians were aware that this study was underway within the ED; hence, these physicians may have been more attentive when collecting blood within the ED than when performing these procedures in the wards. However, this study has continued for more than 2 years; thus, physicians would have become accustomed to being part of this study, which would have reduced potential bias. Second, before the change in policy, physicians were able to select their preferred topical disinfectant for blood sampling; this aspect may have been a confounder, given that multiple studies have shown that contamination is associated more frequently with PVI than with ACHX. However, as shown in Table 3 and the Supplemental table, physicians provided with a choice tended to choose PVI rather than ACHX. Third, this analysis was based on a single-center study, and so might not be generalizable to other hospitals. Nevertheless, our regression discontinuity analysis was robust, leading us to hypothesize that our intervention will be effective in reducing blood culture contamination at other clinical sites.