Impact of Hourly Emergency Department Patient Volume on Blood Culture Contamination and Diagnostic Yield

Abstract

Emergency departments (EDs) are an important diagnostic site for outpatients with potentially serious infections. EDs frequently experience high patient volumes, and crowding has been shown to negatively impact the delivery of early care for serious infections, such as pneumonia. Here, we hypothesized that other important factors in the early care of infectious diseases, the rate of blood culture contamination and the accurate detection of pathogens, would be sensitive to ED operational stress, as proper collection requires fastidious attention to technique and timing. We related all blood samples collected over 1 year and their rates of recovery of likely contaminants and pathogens to the number of patients being cared for in the ED at the time of sample collection. Likely pathogens and contaminants were classified through combined microbiological and manual chart review criteria. Zero-inflated Poisson regression was used to relate crowding to culture results. Blood samples were obtained from 7,586 patients over 82,521 adult and pediatric patient visits. The unadjusted rates of recovering a likely pathogen or a likely contaminant were 8.0% and 3.7%, respectively. Periods of increased crowding (3rd and 4th quartiles of hourly occupancy) were significantly associated (P < 0.01) with increased rates of contamination (relative risk, 1.23 compared to the least busy quartile). Collecting samples for culture during busy times was also associated with a reduced likelihood of recovering a likely pathogen (relative risk, 0.93 compared to the least busy quartile). ED crowding was associated with degraded performance of blood cultures, both increasing the rate of contamination and decreasing the diagnostic yield. Despite considerable efforts to reduce their incidence, contaminated blood cultures continue to be a significant clinical problem. Ongoing multicenter monitoring in the United States places the median rate of contamination at just under 3% (lower national quartile, 2.15%; upper quartile, 3.67%) (1). The clinical and financial impacts of contaminated cultures have been examined by numerous groups; the most recently published results indicate that among patients undergoing blood culture during emergency department (ED) evaluation and subsequent admission to the hospital, a false-positive culture adds an estimated $8,700 (2008 U.S. dollars) and an additional day of hospitalization (2). Excess contamination rates are driven primarily by a lack of operator fastidiousness during the collection process (3). As such, interventions such as dedicated phlebotomy teams, prepackaged blood culture kits, and the use of sterile gloves have helped decrease contamination rates (4, 5).One clinical setting about which little is known regarding blood culture contamination is the emergency department (ED). EDs are an important and common site for initial diagnosis and treatment; more than 136 million visits took place in 2009, the most recent year for which Centers for Disease Control and Prevention data are available (6). Increasingly...

Blood cultures in emergency medical admissions

“…performed in the ED are negative in almost all cases [26], and even when positive, they only identify organisms in a few cases, and rarely alter antimicrobial management [27]. Other studies have shown that the diagnostic ability of blood cultures performed in the ED is high [28]; however, important operational factors determine their effectiveness -for example, lack of knowledge on good sampling practices [29] and ED overcrowding have been shown to degrade the performance of blood cultures, increase contamination rates, and reduce diagnostic yields [30]. A further important factor to consider is the high proportion of elderly and nursing-home residents presenting to the ED.…”

The effect of a quality improvement programme reducing blood culture contamination on the detection of bloodstream infection in an emergency department

“…We were intrigued that most contamination occurred during regular daytime hours, rather than during night shifts. Other studies have found an association between increased departmental activity and BC contamination (Lee et al, 2012;Halverson et al, 2013). We did not match BC sampling times with departmental activity in this study, but this would be a useful component of future work.…”

“…Contamination was defined pragmatically as the presence in BC of low pathogenicity skin commensals (such as coagulase-negative staphylococci, Micrococcus species and Corynebacteria species) in patients not known to have central venous access or indwelling prosthetic material. Other similar studies have used varying definitions of BC contamination, some microbiological (Madeo et al, 2005;Gander et al, 2009;Youssef et al, 2012;Self et al, 2013) and others supplemented with clinical correlation (Schifman et al, 1998;Halverson et al, 2013;Harding and Bollinger, 2013). Our definition was primarily microbiological and was chosen for its simplicity and reproducibility without the need for access to patient records, accepting that it may modestly overestimate true BC contamination.…”

Multidisciplinary team review of best practices for collection and handling of blood cultures to determine effective interventions for increasing the yield of true-positive bacteremias, reducing contamination, and eliminating false-positive central line–associated bloodstream infections

“…Periods of increasing crowding in EDs have been associated with significant increases of BCC, suggesting that lapses in proper collection techniques by health care workers were contributory. 135 Table 3 summarizes studies that have reported successful strategies in reducing contamination rates and other associated outcomes in EDs. 53,71,78,79,[136][137][138][139][140][141][142] A common practice in Pediatric EDs is to obtain a sample for BCs simultaneously when inserting a peripheral intravenous catheter (PIV).…”