Utility of stool samples for the diagnosis of Tuberculosis using GeneXpert MTB/RIF Ultra

Vishal Sharma1, Mohita Gaur1, Anoop Singh1, Anjali1, Chanchal Kumar2, Mandira Varma-Basil2, Anil Chaudhry3, Richa Misra1,4*, Yogendra Singh1*

1Department of Zoology, University of Delhi, Delhi-110007, India; 2Vallabhbhai Patel Chest Institute, University of Delhi, Delhi-110007, India; 3 Rajan Babu Institute of Pulmonary Medicine and Tuberculosis, Kingsway Camp, Delhi, India; 4Sri Venkateswara College, University of Delhi, Delhi-110021, India.                                                                                                                                                 

Tuberculosis (TB) is an air-borne infectious disease caused by Mycobacterium tuberculosis (Mtb). This disease is a persistent problem and the leading cause of death in the developing world. As of now, sputum smear microscopy remains the cornerstone for diagnosing the pulmonary TB (PTB) across the globe. The most frequently used clinical sample for detection of Mtb using this method is sputum. However, difficulty in sputum expectoration in many patients such as HIV cases, women and children, hinders the ease of the method. Moreover, extra-pulmonary TB (EPTB), the rapidly-emerging manifestation of Mtb is not accompanied by coughing or any other symptomatic features commonly seen in TB cases, which makes the clinical diagnosis extremely difficult. The advent of nucleic acid amplification-based next-generation GeneXpert MTB/RIF Ultra assay proved to be a major advancement in diagnosis of EPTB cases with high sensitivity and quick result, although the approach for specimen procurement is still invasive. Thus, using an alternative non-invasive specimen such as stool, which is potentially easier than collecting any other invasive specimen may encourage better attempts at early confirmation of the disease. We hypothesized that swallowed Mtb in case of PTB would be detectable in stool samples; this only occurs during active infection. However, fecal shedding also occurs in EPTB cases. Our results show a moderate sensitivity of stool-Xpert Ultra for EPTB cases (Lymph node and Abdominal) along with high sensitivity for sputum scarce PTB cases with 100% specificity for both cases. This strongly indicates that stools could be used in conjunction with routine diagnostic samples or as an alternative specimen following with diagnosis by microbiological techniques.