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Xpert testing decreased isolation time among suspected TB patients
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Routine Xpert testing of respiratory specimens of patients in airborne infection isolation may significantly decrease the duration of isolation vs. a three-smear microscopy strategy, according to new data.
“While smear microscopy has been effective in reducing health care-associated TB transmission, it has important health system limitations,” researchers wrote in Clinical Infectious Diseases. “Smear microscopy has relatively poor sensitivity for diagnosing active TB, especially in HIV-infected individuals. Specimen processing is labor-intensive, requiring experienced personnel to avoid errors, and is therefore typically performed in batches once daily.”
In the single-center, observational cohort study, researchers evaluated 207 inpatients with presumed pulmonary TB at the University of North Carolina Hospitals, where patients are required to be placed in airborne infection isolation (AII) and provide three sputum samples collected between 8 and 24 hours apart. The specimens were analyzed using routine smear microscopy and culture, as well as with the Xpert MTB/RIF assay (Cepheid), an automated, rapid nucleic acid amplification test endorsed by WHO in 2010 and approved by the FDA in 2013.
Because Xpert was approved for investigational use only at the time of the study, clinicians were masked to the Xpert results. Duration of AII was defined as the study’s primary endpoint, with laboratory processing time, strategy-based tuberculosis detection, sensitivity and specificity established as secondary endpoints.
The researchers found smear microscopy achieved a median AII duration of 68 hours (interquartile range [IQR], 47.1-97.5) In comparison, the one-specimen Xpert attained an AII duration of 20.8 hours (IQR, 16.8-32), the two-specimen Xpert achieved AII duration of 41.2 hours (IQR, 26.6-54.8), and the three-specimen Xpert strategy led to an AII duration of 54 hours (IQR, 43.3-80; P≤.004). Smear microscopy required 2.5 times the median laboratory processing time required by Xpert (P<.001). All six TB cases were captured by the two- and three-specimen Xpert and smear microscopy strategies, whereas one case was missed by the one-specimen Xpert test. There were no observed discrepancies between the strategies in sensitivity or specificity in detecting Mycobacterium TB.
“Since Xpert is now authorized for marketing in the U.S., additional prospective studies in low-burden settings will be important to confirm our observation that a two-specimen Xpert strategy minimizes AII duration, while diagnosing all tuberculosis cases among hospitalized patients with presumptive TB,” the researchers concluded.
Disclosure: The researchers report no relevant financial disclosures.
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