Sputum-Based Molecular Assay Accurately Identifies Culture-Confirmed Tuberculosis


A sputum molecular testing algorithm accurately identified TB and was easily implemented in a center in San Francisco.

Max Salfinger, MD

A sputum-based molecular testing strategy (GeneXpert MTB/RIF) was safe, feasible, easily adopted, and was associated with both clinical and economic benefits in guiding the discontinuation of respiratory isolation for patients undergoing evaluation for active tuberculosis (TB), according to findings from a prospective cohort study published in JAMA Internal Medicine.

“Respiratory isolation is effective for reducing nosocomial TB transmission, but delays care and places a considerable burden on patients, clinicians, and hospitals,” the investigators wrote. “Molecular testing is simpler, faster, and more accurate than conventional microbiologic testing and has been deemed a public health priority, although it has not been widely adopted.”

A total of 621 consecutive patients undergoing a sputum examination for active pulmonary TB during a 2-year period at a San Francisco hospital were included in the prospective analysis. Study investigators only included patients who had molecular testing ordered and completed and measured the accuracy of the testing strategy in reference to mycobacterial culture.

Additionally, the investigators evaluated the duration of each testing and isolation process component, the length of hospital stay, the average days in isolation and the hospital, and the average cost associated with the molecular testing algorithm.

In the period prior to implementation of the molecular testing, a total of 301 patients had ≥1 sputum microscopy and culture ordered, with 233 (77%) patients having a rapid TB testing evaluation process completed. Comparatively, a total of 234 patients out of 320 patients after implementation had a molecular test ordered, whereas 98% of patients received results for ordered tests.

Approximately one-quarter of participants were women (26%), and the median age was 54 years (interquartile range, 44 to 63 years). In the 7 patients with culture-confirmed TB, the molecular testing algorithm was associated with an accurate diagnosis. Additionally, the algorithm resulted in the exclusion of TB in the patients with Mycobacterium tuberculosis (MTB) culture-negative results (n = 251).

The investigators observed significant reductions from pre- to post-implementation of the algorithm in the median duration to final rapid test results (39.1 vs 22.4 hours; P <.001), discontinuations of isolation (2.9 vs 2.5 days; P =.001), as well as reduced hospital discharge (6.0 days vs 4.9 days; P =.003). Significant reductions were also observed in cost, with the testing strategy associated with an average cost-savings of $13,347 per isolated TB-negative patient.

The authors highlight several limitations of the study’s design, including its use of patient data from a single center, which may limit generalizability of the findings.

In an accompanying editorial, Max Salfinger, MD, commented on how these findings may impact clinical practice. “Twenty years after the first US Food and Drug Administration (FDA)-approved NAAT, the evidence showed that clinicians and infection preventionists, as well as hospital administrators, should work with all stakeholders to identify barriers at their institution (eg, outdated electronic ordering algorithms, not acknowledging system-wide savings when only focused on laboratory expense) preventing a wider implementation of NAAT testing,” he wrote. “In addition, they should validate this new algorithm, so their institutions can reap the potential substantial savings that result from using a NAAT for patients with possible TB in airborne infection isolation.”

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