Abstract
GeneXpert MTB/RIF (Xpert) assay has been endorsed for the diagnosis of pulmonary TB due to its high sensitivity and specificity for culture positive TB. There is no doubt that Xpert could not be more sensitive than mycobacterial culture, while the positive rate of Xpert among sputum samples was higher than that of mycobacterial culture in our laboratory. We therefore carried out a prospective study to determine a potential explanation for this unexpected result regarding the clinical use of Xpert. Overall, a total of 558 patients meeting inclusion criteria were enrolled in final analysis between August 2017 and September 2017 in Beijing Chest Hospital. The overall positive rate of Xpert among sputum samples was 45.9% (256/558), which was significantly higher than that of liquid culture (33.4%, 184/558; P < 0.01). The percentage of culture negative result in salivary sputum was significantly higher than that in mucoid sputum [odds ratio (OR): 5.04, 95% confidence interval (95% CI): 2.74–9.28; P < 0.01]. In addition, the TB cases having previous treatment history had a higher proportion of culture negative result than new cases (OR: 4.26, 95% CI: 1.61–11.28; P = 0.01). In conclusion, the results of this study demonstrate that Xpert outperforms mycobacterial culture in detecting MTB from salivary sputum. In addition, the previously treated patients are more likely to yield negative culture results. Our data will provide important hints to formulate an appropriate diagnostic algorithm for pulmonary tuberculosis based on the appearance of sputum samples.
Highlights
Tuberculosis, caused by Mycobacterium tuberculosis complex (MTBC), is the leading cause of morbidity and mortality from an infectious disease worldwide, with an estimated 10.4 million new cases and 1.3 million deaths in 2016 (WHO, 2017)
Statistical analysis revealed that the TB cases having previous treatment history had a higher proportion of culture negative result than new cases (OR: 4.26, 95% confidence interval (95% CI): 1.61–11.28; P = 0.01)
We observed that Xpert outperformed mycobacterial culture in the detection of MTB from salivary sputum
Summary
Tuberculosis, caused by Mycobacterium tuberculosis complex (MTBC), is the leading cause of morbidity and mortality from an infectious disease worldwide, with an estimated 10.4 million new cases and 1.3 million deaths in 2016 (WHO, 2017). China has achieved great progress in TB control by the implementation of effective TB control strategy, the low detection rate of bacteria-positive TB cases poses a new challenge that hampers efforts at tuberculosis control [1]. According to the analysis of nationwide data, only 30% of the reported TB patients had positive laboratory evidence in this country, which is significantly lower than the global average rate of 50% (WHO, 2017). This unsatisfactory situation highlights the urgent need to develop and employ higher sensitivity assays for identifying TB patients. Several recent analyses suggest that Xpert yields promising efficacy in detecting extrapulmonary TB (EPTB), which facilitates the formulation of WHO guidelines for the application
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