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Diagnostic accuracy of upper airway swabs and saliva with Xpert MTB/RIF Ultra for the detection of tuberculosis in adults

M de Vos(9) N van Hung(1) C A Ugarte-Gil(2,3) H Cox(4) K Ali(2) N Hapeela(4) M Joloba(5) R Post(6) S Kim(6) S Kennedy(8) M Ruhwald(9) J Ellnor(7) A Penn-Nicholson(9) S Dorman(8)

1:National Tuberculosis Reference Laboratory, National Tuberculosis Control Programme, National Lung Hospital, Hanoi, Viet Nam; 2:Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, 15102, Peru; 3:School of Medicine, Universidad Peruana Cayetona Heredia, Lima, 15102, Peru; 4:Division of Medical Microbiology, Department of Pathology, University of Cape Town, Cape Town, 7925, South Africa; 5:Department of Microbiology, School of Biomedical Sciences, Makerere University, Kampala, 7062 Uganda; 6:Department of Biostatistics, Frontier Science Foundation, Madison, WI 53711 and Brookline, MA 02446, USA; 7:Center for Emerging Pathogens, Department of Medicine, Rutgers-New Jersey Medical School, Newark, NJ, USA. Newark, 07103, USA; 8:Department of Medicine, Medical University of South Carolina, Charleston, 29425, USA; 9:FIND, Geneva, 1202, Switzerland

To regain progress lost during the COVID-19 pandemic and reduce the global burden of tuberculosis (TB), diagnostic innovations are critically needed. Upper airway swabs offer a promising alternative sample type to sputum as collection is rapid, non-invasive and can be obtained from non-sputum productive patients.

As part of the FEND-TB multicentre clinical study (adults, symptomatic for TB), we assessed the diagnostic accuracy of Xpert MTB/RIF Ultra (Ultra) for the detection of pulmonary TB using saliva and swabs sampled from four different upper airway sites. Swabs were collected in 1.2mL PBS buffer and Ultra testing was done using the manufacturer’s instructions.  Using the composite of sputum culture and/or Ultra as the microbiological reference standard (MRS), 60 sputum smear-positive and 30 smear-negative MRS-positive, and 30 MRS-negative participant samples were evaluated.  Upper airway swabs from smear-positive participants had Ultra sensitivity of 88% (95% CI 80-95), 67% (95% CI 50-79), 74% (95% CI 57-85) and 55% (95% CI 38-72) from tongue dorsum, cheeks and gums, combined tongue-cheeks-gums, and mid-turbinate nasal swabs. Specificity was 100% for all swab types. In smear-negative, sensitivity was 16.7% (95% CI, 7.3-33.6) from the tongue dorsum. In saliva, sensitivity was 100% (95%CI 87.5-100) in smear-positive and similarly poor in smear-negative cases (17.6% (95% CI, 7.7-35.4)).

The poor performance of oral swabs from smear-negative participants may be due to processing where only 55% of the total sample was tested. We will further discuss optimization of the Ultra workflow, determine the stability of tongue swabs and feasibility of testing serially collected swabs.

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