The study was carried out in the Pediatric Pulmonology Division of All India Institute of Medical Sciences, New Delhi, between January 2015 and October 2016. The study was approved by Institute Ethics Committee. The criteria for probable pulmonary TB were [13]: Any of the clinical symptoms: cough and/or fever >2 weeks, weight loss, lethargy; History of contact with adult TB case or positive Mantoux test; and Chest X-ray suggestive of tuberculosis.

Flexible bronchoscopy was performed under conscious sedation with midazolam and fentanyl, after receiving written informed consent from parents. After inspecting all the bronchial segments, BAL samples were collected from the lung segments showing abnormal lesions on X-ray film or CT scan of chest.

BAL samples were analyzed by smear microscopy, Xpert MTB/RIF (Cepheid, Sunnyvale CA, USA), MGIT-960 (Becton, Dickinson and Co, New Zealand) culture and drug susceptibility testing (DST).

Statistical analysis: Sensitivity for Xpert MTB/RIF assay on BAL fluid for the diagnosis of probable and confirmed pulmonary TB were calculated by considering the clinico-radiological diagnosis and liquid culture, respectively as separate gold standards.

Forty-one children (22 boys) with median (IQR) age of 10 (5.5, 13) years underwent diagnostic bronchoscopy during the study period; none were known to be HIV seropositive (Table I). Drug-resistant pulmonary TB was suspected in 12 children; nine of them had treatment failure and three had relapsed after treatment. Two patients had contact with MDR-TB patients.

TABLE  I	Characteristics of Children with Probable Pulmonary Tuberculosis (N=41)

Xpert MTB/RIF, MGIT culture and smear were positive in 24 (58.5%), 10 (24.4%), and 4 (9.7%) BAL samples, respectively (Table I). Eleven (26.8%) were culture confirmed TB (BAL=10, sputum=1). Comparison of Xpert MTB/RIF in BAL fluid with MGIT culture and ZN staining is presented in Table II.

TABLE II 	Comparison of Bronchoalveolar  Lavage Xpert in Probable Pulmonary Tuberculosis (N=41) and Suspected 
Drug Resistant Pulmonary Tuberculosis (N=12) with Culture and ZN Smear 

Xpert MTB/RIF and MGIT culture in BAL fluid were positive in 58.5% (24/41) and 24.4% (10/41), respectively. The sensitivity and specificity of BAL Xpert MTB/RIF in detecting culture confirmed TB was 81.8% (9/11) and 50% (15/30), respectively; positive- and negative-predictive values were 37.5% (9/24) and 88.2% (15/17), respectively.

Xpert MTB/RIF could identify an additional 15 (36.6%) cases, where all other microbiological investigations were negative.

Among suspected MDR-TB patients, drug resistance was identified in three (27.3%) by BAL MGIT culture and DST. However, rifampicin resistance by Xpert MTB/RIF in BAL fluid was documented in two patients (2/11) (Table II). The three confirmed drug resistant patients were started on second line anti-TB drugs. Three additional children were positive with BAL Xpert MTB/RIF over the MGIT culture, though they were rifampicin sensitive. These patients were started on Category II ATT.

In this diagnostic study, we observed that Xpert MTB/RIF assay on BAL samples has good sensitivity in both probable (58.5%) and confirmed (81.8%) pulmonary tuberculosis in children. BAL Xpert resulted in additional diagnostic yield and also in the rapid detection of drug resistance in children with probable pulmonary tuberculosis.

The present study is limited by small sample size. We could not estimate specificity for BAL Xpert assay in probable pulmonary TB as the control group of children without tuberculosis were not enrolled.

In our study, sensitivity of BAL Xpert MTB/RIF was higher than culture among sputum/GA smear negative probable pulmonary TB patients. Similarly, Walters, et al. [11] found higher sensitivity of BAL Xpert MTB/RIF in children with suspected complicated pulmonary TB (78%) as compared to culture (64%) [11]. A study done in Chinese children [12] also showed higher sensitivity of BAL Xpert MTB/RIF (53%) as compared to culture (28.9%). In our study, we found sensitivity of 81.8% for Xpert MTB/RIF on BAL samples in culture-confirmed cases, which is similar to that reported in adults earlier (78%-92.3%) [11,14-15].

One of the strengths of Xpert MTB/RIF assay is to detect rifampicin resistance within same day, which can facilitate early diagnosis and treatment of MDR TB. In the present study, BAL Xpert MTB/RIF successfully identified two of the three rifampicin resistant cases. In case of suspected drug resistant TB, MGIT culture may still be the preferred test and Xpert assay may be used as add-on test for rapid detection of these cases.

We conclude that BAL Xpert MTB/RIF assay may aid in clinical management of probable pulmonary tuberculosis in children by improving case detection and enabling the treating physician to take early decisions.

Acknowledgements: AM is an Early Career Fellow – Wellcome Trust/DBT India Alliance and would like to acknowledge Wellcome Trust/DBT India Alliance for support.

Contributors: IS: Data collection, data analysis and writing of manuscript; AM: Analysis of data and writing of manuscript; HG: Microbiology investigations and reviewing of manuscript; MS: Data collection, writing of manuscript; RL: Data analysis, manuscript writing; KRJ: Data collection and writing of manuscript; UBS: Microbiology investigations and reviewing of manuscript; SKK: Data collection, data analysis and writing of manuscript and will act as guarantor for the study.

Funding: None; Competing Interest: None stated.