Novel Test Quickly Identifies Five Common Bacteria in Bloodstream Infections

Nicola M. Parry, DVM

May 14, 2019

A novel culture-independent diagnostic test showed high sensitivity and specificity in identifying bloodstream infections (BSIs) caused by five common bacteria, a study published online May 13 in the Annals of Internal Medicine shows.

Experts caution, however, that it remains to be seen whether the test will improve patient outcomes.

The T2Bacteria Panel (T2 Biosystems) is the first culture-independent test approved by the US Food and Drug Administration (FDA) for identifying BSI-causing bacteria directly from whole blood, report Hong Nguyen, MD, University of Pittsburgh Medical Center, Pennsylvania, and colleagues.

The technology combines polymerase chain reaction amplification and T2 MRI to detect five important ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli).

These bacteria constitute about half of all organisms recovered from positive blood cultures and tend to exhibit multidrug resistance.

"[T]he T2Bacteria Panel accurately identified or excluded BSIs caused by 5 common ESKAPE pathogens in about 4 to 8 hours versus about 24 to 72 hours and 5 days, respectively, for blood cultures," the authors write.

In their prospective study, Nguyen and colleagues investigated the performance of the T2Bacteria Panel in diagnosing suspected BSIs in adults, comparing its performance with that of a single set of blood cultures.

The study included 1427 patients for whom blood cultures were performed as standard of care in 11 US hospitals. The T2Bacteria Panel was used in combination with a single set of cultures.

Overall, the investigators identified the ESKAPE bacteria from 3% of patients in blood cultures; with T2Bacteria testing, they identified bacteria in 13%.

From the start of blood culture incubations, the mean time to positivity was 38.5 hours, and the mean time to species identification was 71.7 hours.

In comparison, the mean time to results using the T2Bacteria Panel ranged from 3.61 to 7.70 hours, depending on the number of samples tested.

There was agreement between the two tests in 90% of samples and disagreement in 10%.

In cases of proven BSI, the T2Bacteria Panel had a sensitivity of 90% (95% confidence interval [CI], 76% – 96%) and a specificity of 90% (95% CI, 88% – 91%). Its negative predictive value was 99.7%.

In patients whose blood cultures were negative for target bacteria, 10% received a positive result on testing with the T2Bacteria Panel; 60% of these (88 of 146) were associated with probable (n = 62) or possible (n = 26) BSIs.

If probable BSIs were assumed to be actual BSIs that blood culture failed to identify, the T2Bacteria Panel had a per-patient specificity of 94%. This rose to 96% if both probable and possible BSIs were assumed to be actual BSIs.

"Overall, T2Bacteria results correlated well with those from blood cultures," the authors write.

They emphasize that this new test will most likely be useful if used alongside blood and nonblood cultures and if clinicians consider its results in the context of patients' clinical status and antibiotic use.

A key priority is to now determine what role the T2Bacteria Panel will play in clinical practice and its effect on patient outcomes, conclude Nguyen and colleagues.

In an accompanying editorial, David A. Weinrib, MD, and Gerald A. Capraro, PhD, both from Atrium Health, Charlotte, North Carolina, write that the results of this study parallel those presented to the FDA to support the request to approve the T2Bacteria Panel. That approval was based on the "substantial equivalence" of the T2Bacteria Panel to the FDA-approved T2Candida Panel.

Nevertheless, the editorialists stress that the study fails to address whether the new test improves outcomes for patients with suspected BSI or sepsis.

"The authors note that clinicians were not informed of the results in real time," write Weinrib and Capraro.

"It is also unknown whether detection of an organism by the T2Bacteria Panel alone indicates clinically significant bacteremia that would change the duration of antibiotic therapy compared with if the organism were detected only in urine, sputum, or a wound," the editorialists write.

Thus, there is a need for outcomes studies to assess the potential benefit of this new test in managing this patient population. These studies should investigate questions such as whether the test can improve 30-day survival, decrease the length of hospital stays, or reduce the number of days of antibiotic therapy per 1000 patient-days, the editorialists add.

Cost is another important factor to consider, they note, regarding adopting any new technology.

"The T2Bacteria Panel targets only 5 clinically relevant bacteria, and whether this will significantly reduce costs or benefit patients with suspected BSI and sepsis has yet to be proved," conclude Weinrib and Capraro.

The study was supported by T2 Biosystems. The original articles contain full listings of the authors' and editorialists' relevant financial relationships.

Ann Intern Med. Published online May 13, 2019. Abstract, Editorial

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