Xpert test may eliminate excess isolation time in TB evaluations
Using a single sputum molecular test in place of serial sputum smear microscopy for inpatients undergoing tuberculosis evaluation may eliminate unnecessary time isolation, according to researchers from the University of California, San Francisco.
The GeneXpert MTB/RIF (Xpert, Cepheid) nucleic-acid amplification test (NAAT) could save as many as 45 hours in unnecessary isolation compared with microscopy, the researchers found.
“Time and cost savings would likely be even greater in hospitals that require three negative sputum smear results prior to the discontinuation of respiratory isolation,” they wrote in Clinical Infectious Diseases. “Several other analyses have demonstrated that Xpert and other NAATs for this purpose could result in considerable cost-savings.”
The researchers prospectively followed 139 inpatients who underwent TB evaluation. They performed smear microscopy and Xpert testing on the concentrated sputum and determined the diagnostic accuracy for both. They also compared the turnaround time for isolation time for microscopy and for Xpert testing on both concentrated and unconcentrated sputum.
They found that serial sputum smear microscopy and a single concentrated sputum Xpert test had the same sensitivity (89%) and similar specificity: 99% for the microscopy and 100% for the Xpert test. Overall, the processing time from admission to final negative smear diagnosis by microscopy was a median of 66 hours.
In a hypothetical analysis, the median time from admission to Xpert result using concentrated sputum was an estimated 34 hours, which would have reduced time in unnecessary isolation by a median of 35 hours. With the unconcentrated sputum Xpert testing, the median time from admission to Xpert result would have been 4.5 hours, reducing the time spent in unnecessary isolation by a median of 45 hours.
“These data, combined with the well-established greater sensitivity of Xpert and its benefits to patients in reduced time spent in isolation, should lead to a re-evaluation of current guidelines which recommend sputum smear microscopy for triage of respiratory isolation rooms,” the researchers wrote.
Disclosure: The researchers report no relevant financial disclosures.