Editorial Commentary: Xpert MTB/RIF Testing for Individuals With Presumed Tuberculosis: Implications for Infection Control and Rapid Tuberculosis Detection in the United States

Despite recent declines in incidence, tuberculosis remains a significant public health problem in the United States, with almost 10 000 new cases each year [1]. As the disease becomes less common in the United States, diagnostic delays occur because of diverse clinical presentations and suboptimal diagnostic tests. Sputum smear microscopy to detect acid-fast bacilli (AFB) remains widely used for rapid detection of pulmonary tuberculosis, but sensitivity is poor; AFB smear microscopy does not differentiate between tuberculosis and nontuberculous mycobacteria, necessitating additional testing for speciation. Mycobacterial culture remains the most sensitive diagnostic modality, but may require weeks to detect growth of M. tuberculosis; even with mycobacterial culture, multiple specimens are often needed to identify cases of paucibacillary disease. Evaluating individuals with presumed tuberculosis thus remains resource-intensive, and requires infection control measures to mitigate the risk of tuberculosis transmission during the evaluation process. Centers for Disease Control and Prevention (CDC) guidelines for prevention of tuberculosis transmission in healthcare settings recommends that patients under evaluation for tuberculosis be placed in airborne infection isolation (AII), preferably in a negative-pressure ventilation room. Personal respiratory protective devices (eg, N95 masks) are recommended for healthcare workers, and isolation is maintained until 3 serial AFB sputum smears collected 8–24 hours apart are negative [2]. Although negative sputum smears do not exclude a diagnosis of tuberculosis, they suggest a lower degree of infectiousness. Such principles are effective at reducing nosocomial transmission of tuberculosis in healthcare facilities, but are time-consuming and costly. The number and availability of AII rooms is often limited, so finding methods to efficiently and rapidly exclude infectious tuberculosis from the differential diagnosis is a priority. In low-tuberculosis-prevalence settings, only a small percentage of individuals who are isolated ultimately receive a tuberculosis diagnosis. With the advent of new diagnostic technologies, novel approaches to tuberculosis detection and infection control are now being explored. Despite current CDC recommendations that nucleic acid amplification tests (NAATs) be performed on at least 1 respiratory specimen from all patients evaluated for tuberculosis, molecular testing for tuberculosis in the United States is underutilized, due to lack of awareness or due to costs and logistical considerations [3]. The use of NAATs has the potential to rapidly identify infectious tuberculosis patients and exclude those at lower risk for tuberculosis transmission. In this issue of Clinical Infectious Diseases, Chaisson et al evaluate the potential impact of Xpert MTB/RIF assay (“Xpert”; Sunnyvale, California) implementation on reducing testing time and duration of AII utilization for patients with signs or symptoms of tuberculosis. Xpert MTB/RIF is a cartridge-based, fully automated NAAT that detects tuberculosis (and rifampin resistance) within 2 hours and has recently received World Health Organization endorsement and US Food and Drug Administration approval for tuberculosis diagnosis [4, 5]. The test has improved sensitivity over smear microscopy (identifies nearly all smear-positive tuberculosis cases and approximately 70% of smear-negative pulmonary tuberculosis cases), and has very high specificity [6]. Sensitivity remains reduced compared with mycobacterial Received 22 July 2014; accepted 29 July 2013. Correspondence: Maunank Shah, MD, PhD, Johns Hopkins University School of Medicine, 725 N Wolfe St, PCTB Bldg 224, Baltimore, MD 21205 (mshah28@jhmi.edu). Clinical Infectious Diseases © The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals. permissions@oup.com. DOI: 10.1093/cid/ciu626