Diagnostic Yield of Xpert MTB/RIF Assay Determined by Clinical Presentation in Childhood Intra-Thoracic Tuberculosis

Background: Diagnosis of Intra-thoracic Tuberculosis (ITTB) in children is challenging. Contribution of Xpert MTB/RIF assay to diagnosis of suspected ITTB and multi-drug resistant TB (MDR-TB) was evaluated. Methods: Children with suspected ITTB (395) were subjected to gastric aspirates and induced-sputum twice.Samples were tested by Ziehl-Neelsen stain, Xpert MTB/RIF-assay and MGIT-960 culture. Subjects were grouped as Confirmed, Probable and No-TB and classified as progressive primary disease (PPD, lung parenchymal lesion/pleural effusion/ pneumothorax) and primary pulmonary complex (PPC, hilar lymphadenopathy) on Chest X-ray. Findings: Of children with confirmed TB 51(12.9%), probable TB 306(77.4%) and No-TB 38(9.6%),11(2.7%) were smear positive, 98(24.8%) Xpert MTB/RIF positive and 51(12.9%) culture positive. Xpert MTB/RIF detected 42/51 culture confirmed cases (sensitivity 82% and NPV 97%) and rifampicin resistance in additional 5 cases. Culture detected more children presenting as PPD (p<0.001).Lung parenchymal involvement was seen in 37/42(88%) Confirmed TB, and 51/56(91%) Probable TB children detected by XpertMTB/RIF. Interpretation: Xpert MTB/RIF improved diagnosis by two-fold, and increased detection of MDR-TB. Both liquid culture and Xpert MTB/RIF proved to be more useful in children with PPD. Laboratory diagnosis of PPC is difficult due to pauci bacillary/localised disease. Microbiological tests cannot be blamed alone for poor yield in pediatric TB. Funding: ICMR Grant no. (Grant: 5/8/5/9/2012/ECD-I);AIIMS Intramural Grant. Declaration of Interests: Authors declare no conflicts. Ethical Approval: Study was approved by the Ethics Committee (IEC-IEC/NP-19412012 & RP-ll/2012), All India Institute of Medical Sciences, New Delhi. Consent was taken from the parents/guardians of all the study subjects.