New nonculture panel test accurately identified targeted bacteria in bloodstream infections

The test provided results faster than blood cultures in the industry-funded study, but it's not clear how its use would affect prescribing of antibiotics or patient outcomes, an accompanying editorial noted.

A new bacteria panel accurately diagnosed bloodstream infections caused by five common bacteria more quickly than cultures, a recent industry-funded study found.

The prospective study included 1,427 patients at 11 U.S. hospitals for whom blood cultures were ordered from Dec. 8, 2015, through Aug. 4, 2017. The performance of the T2Bacteria Panel, a direct-from-blood, nonculture test that identifies five types of bacteria (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli) was compared to a single set of blood cultures. The study was funded by the test's manufacturer, T2 Biosystems. Results were published by Annals of Internal Medicine on May 14.

Results were positive for the targeted bacteria in 3% of blood cultures and 13% of the panel tests. The blood cultures took a mean of 38.5 hours (SD, 32.8) for positive results and 71.7 hours (SD, 39.3) for species identification. With the new test, the mean time to species identification was 3.61 (SD, 0.2) to 7.70 (SD, 1.38) hours, depending on the number of samples tested. For proven bloodstream infections, the test's sensitivity and specificity were both 90%. The negative predictive value was 99.7%. Ten percent of the samples had a negative blood culture but a positive test result; however, 60% of these were considered probable or possible bloodstream infections, based on a composite of clinical findings, blood culture results at other times, or culture results from nonblood sites. The authors noted that active antibiotic use was more common in these cases with discordant results, suggesting that the test might have particular value in patients already on antibiotics.

The study was limited by the low prevalence of positive blood cultures for the studied bacteria (only 39 out of 1,427 samples), the authors said. They also wrote that the test “should always be collected in conjunction with blood culture specimens because cultures identify bacteria not included in the panel and yield organisms for phenotypic antibiotic susceptibility testing” and “interpreted with careful consideration of patients' clinical status and antibiotic use.”

An accompanying editorial raised a number of other concerns about the test's clinical utility. “This study does not address whether the T2Bacteria Panel adds value to the management of patients with suspected BSI [bloodstream infection] or sepsis,” the editorialists said. Future research on the panel should assess whether its use shortens time to antibiotic therapy, time on therapy, or length of stay, as well as the impact on survival, laboratory workflows, and cost, the editorial said.