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ORAL SWAB ANALYSIS (TB-OSA) FOR NON–SPUTUM-BASED TB DIAGNOSIS IN KENYA
Sylvia LaCourse1, Rachel Wood1, Evans Seko2, Gregory S. Ouma2, Barbra A. Richardson1, Grace John-Stewart1, Gerard Cangelosi1
1University of Washington, Seattle, WA, USA,2Kenya Medical Research Institute, Kisumu, Kenya
Despite recent advances in rapid TB diagnostics, sample collection remains challenging in those unable to produce sputum. In published proof-of-concept data, oral swab analysis (OSA) detected M. tuberculosis in 90% of HIV-negative Xpert+ adult TB cases in South Africa, with 100% specificity in negative controls. A larger, follow-on evaluation in the same South African population found 92% sensitivity and 92% specificity relative to sputum Xpert. We evaluated OSA performance in HIV-infected and HIV-uninfected TB suspects in Kenya.
One hundred Kenyan TB suspects (cough >2 weeks, plus >1 additional symptom of fever, night sweats, or weight loss) >13 years of age had oral swabs then sputum for Xpert and culture collected at enrollment and consecutive morning visit. Cryopreserved swabs underwent Mtb DNA extraction and qPCR analysis targeting IS6110 insertion sequence. A predetermined threshold Cq <38 was considered positive (lower Cq indicating a stronger more positive signal). OSA performance was assessed compared to a reference of Xpert or culture. OSA mean Cq values were compared using t-tests.
Of 94 participants enrolled with oral swab results, median age was 38 years (IQR 29-44), 48.9% were female, 54.3% were HIV-infected, and 20.1% with history of TB. Among 51 HIV+, 86.3% were on ART and 9.5% had ever received isoniazid preventive therapy (IPT). Nineteen TB cases were identified (18 Xpert/culture+, 1 culture+ only). OSA sensitivity was 68.4% (13/19) with 82.7% (62/75) specificity overall, and 83.3% (5/6) sensitivity and 75.6% (34/45) specificity among HIV-infected. Performance improved on subsequent morning visit samples compared to Xpert alone (sensitivity 80.0% [12/15], specificity 92.3% [60/65]. Mean OSA Cq was stronger (indicated by lower Cq) among Xpert+ vs. Xpert- participants (35.1 +0.8 vs. 37.9 +1.0 SD, p=0.05) and at subsequent morning vs. enrollment visit among OSA+/TB+ (32.5 +2.4 vs. 34.9 +2.6 SD, p=0.008).
In this analysis, performance appeared reduced compared to previous analyses, possibly due to differences in setting, population, and/or study design. Despite the lower performance compared to sputum-testing methods, OSA provides a promising means of TB detection for populations that are unable to produce adequate sputum including those who are HIV-infected.