Study targets hospital blood culture use toward stewardship

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Individual hospitals should track both blood culture (BC) use and positivity rates over time, and establish benchmarks to improve blood culture stewardship, suggests a study published January 15 in JAMA Network Open.

Led by researchers from the Johns Hopkins University School of Medicine in Baltimore, a team of researchers in pathology, microbiology, infection control, and quality assurance investigated blood culture use rate in U.S. medical and medical-surgical intensive care units (ICUs) and wards as COVID-19 hospitalization surged up and down after September 1, 2019. 

The team from institutions around the U.S. also examined blood culture positivity, single blood cultures, blood culture contamination, and minimum threshold for blood culture use where blood culture positivity would be optimized. 

"Concerns point to the need for improved BC stewardship, which may include establishing a benchmark for BC use that allows individual institutions to identify opportunities to improve," stated Dr. Valeria Fabre from the division of infectious diseases at Johns Hopkins and colleagues. 

"The data from this study may help inform initiatives to reduce unnecessary blood culture use while maintaining an acceptable blood culture positivity target," the authors noted, adding that blood culture use benchmarks in U.S. hospitals have not been defined. 

The work is important because blood culturing is used so extensively to diagnose bloodstream infections, and a large portion of blood cultures are collected inappropriately or in patients with a low risk of a bloodstream infection, according to the researchers. 

Focusing on clinical areas with high blood culture use volume, researchers performed a retrospective cross-sectional evaluation of blood culture use in hospital units between September 1, 2019, and August 31, 2021, and analyzed the data last year. 

Forty-eight hospitals in 19 states and the District of Columbia provided data for 362,327 blood cultures -- in all, 292 adult units comprising 27 medical ICUs, 35 medical-surgical ICUs, 121 medical wards, and 109 medical-surgical wards. 

Among the statistics, overall hospital patient days ranged from nearly 300,000 in medical and medical-surgical ICUs to upwards of 2 million in medical and medical-surgical wards. Emergency department and oncology were not included.

Adjusted blood culture use means (per 1,000 patient days) were 273.1 for medical ICUs; 146.0 for medical-surgical ICUs; 80.3 for medical wards; and 65.1 for medical-surgical wards 

Points of interest from the study include:

  1. Of the 292 units, 97% had a mean blood culture contamination rate within 3% of the recommended threshold, and 51% were within 1%.
  2. There were no statistically significant differences in adjusted mean blood culture positivity: 6.5% for medical ICUs, 6.2% for medical-surgical ICUs, 7.3% for medical wards, and 5.6% for medical-surgical wards.
  3. 8% of blood cultures were polymicrobial.
  4. The most common organisms identified in blood culture contamination were coagulase-negative Staphylococci.
  5. The most common pathogen identified in positive blood cultures was S. aureus.

Importantly, Fabre and colleagues estimated minimum thresholds for hospital blood culture use as the following:

  • 120 per 1,000 patient-days for medical ICUs
  • 80 per 1,000 patient-days for medical-surgical ICUs
  • 30 per1000 patient-days for medical-surgical wards 

They said blood culture use below these thresholds represents undertesting. Furthermore, they added that overtesting (testing patients unlikely to have a bloodstream infection) and blood collection practices could be improved as blood culture use remains a cause of unnecessary antibiotic use and healthcare use. 

"Clinicians’ main hesitation to engage in BC stewardship has been concern for missing an infection; therefore, having a minimum BC use threshold could be helpful," noted the team. "Individual hospitals should track both BC use and BC positivity rates over time to understand assessments of opportunity and the effects of efforts to improve BC use and patient selection." 

Read the full report here.

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