Comparing Tuberculosis Diagnostic Yield in Smear/Culture and Xpert® MTB/RIF-Based Algorithms Using a Non-Randomised Stepped-Wedge Design

• Published in: PloS one Vol. 11; no. 3; p. e0150487
• Main Authors: Naidoo, Pren, Dunbar, Rory, Lombard, Carl, du Toit, Elizabeth, Caldwell, Judy, Detjen, Anne, Squire, S. Bertel, Enarson, Donald A., Beyers, Nulda
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.03.2016; Public Library of Science (PLoS)
• Subjects: Adolescent; Adult; Aged; Aged, 80 and over; Algorithms; Biology and Life Sciences; Child; Child, Preschool; Childrens health; Clinical Laboratory Techniques - methods; Culture; Diagnostic systems; Diagnostic tests; Female; Health sciences; HIV; Human immunodeficiency virus; Humans; Infant; Laboratories; Lung diseases; Male; Medical diagnosis; Medicine; Medicine and Health Sciences; Microscopy; Middle Aged; Multidrug resistant organisms; People and places; Primary care; Randomization; Regression models; Research and Analysis Methods; Risk; Sensitivity and Specificity; Smear; South Africa; Sputum; Sputum - microbiology; Tuberculosis; Tuberculosis, Multidrug-Resistant - diagnosis; Tuberculosis, Pulmonary - diagnosis; Tutu, Desmond; Wedges; Yield; Young Adult; South Africa; France
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0150487

Primary health services in Cape Town, South Africa. To compare tuberculosis (TB) diagnostic yield in an existing smear/culture-based and a newly introduced Xpert® MTB/RIF-based algorithm. TB diagnostic yield (the proportion of presumptive TB cases with a laboratory diagnosis of TB) was assessed using a non-randomised stepped-wedge design as sites transitioned to the Xpert® based algorithm. We identified the full sequence of sputum tests recorded in the electronic laboratory database for presumptive TB cases from 60 primary health sites during seven one-month time-points, six months apart. Differences in TB yield and temporal trends were estimated using a binomial regression model. TB yield was 20.9% (95% CI 19.9% to 22.0%) in the smear/culture-based algorithm compared to 17.9% (95%CI 16.4% to 19.5%) in the Xpert® based algorithm. There was a decline in TB yield over time with a mean risk difference of -0.9% (95% CI -1.2% to -0.6%) (p<0.001) per time-point. When estimates were adjusted for the temporal trend, TB yield was 19.1% (95% CI 17.6% to 20.5%) in the smear/culture-based algorithm compared to 19.3% (95% CI 17.7% to 20.9%) in the Xpert® based algorithm with a risk difference of 0.3% (95% CI -1.8% to 2.3%) (p = 0.796). Culture tests were undertaken for 35.5% of smear-negative compared to 17.9% of Xpert® negative low MDR-TB risk cases and for 82.6% of smear-negative compared to 40.5% of Xpert® negative high MDR-TB risk cases in respective algorithms. Introduction of an Xpert® based algorithm did not produce the expected increase in TB diagnostic yield. Studies are required to assess whether improving adherence to the Xpert® negative algorithm for HIV-infected individuals will increase yield. In light of the high cost of Xpert®, a review of its role as a screening test for all presumptive TB cases may be warranted.