Background: Line probe assay (LPA) is used for first-line drug susceptibility testing (DST) of smear-positive pulmonary tuberculosis (TB) patients. For extra-pulmonary (EP) and smear-negative TB patients, the samples are inoculated in culture and isolates of Mycobacterium tuberculosis (MTB) are tested on LPA. This results in considerable delay and loses the benefit of rapid diagnostics. In the present study, smear-positive EP specimens were tested directly on LPA and their results were compared with LPA conducted on culture isolates of same specimens.
Method: All EP specimens received from different parts of Gujarat State in 2014 were subjected to ZN smear microscopy and inoculated on liquid culture. Smear-positive samples were directly tested with LPA. Simultaneously, culture isolates of MTB were also subjected to LPA. Results of LPA conducted on both direct specimen and culture isolates were compared.
Result: Of 391 extra-pulmonary specimens, 177 were smear positive and tested directly on LPA. Simultaneously, 88 were culture positive and their isolates were tested on LPA. With LPA on direct specimen, 127 (32%) had valid results with median time to diagnose rifampicin resistance of 5 days (IQR 2-7). In comparison, 88 (23%) specimens had valid results with culture isolates tested on LPA and with longer turnaround time (18-40 days). Among 51 samples, with valid LPA results both on direct samples and isolates, 50 (98%) had concordance for drug resistance pattern.
Conclusion: There is advantage in testing extra-pulmonary smear-positive samples directly on LPA and the results would also be available rapidly.
Keywords: Drug susceptibility test; Extra-pulmonary tuberculosis; Line probe assay; Revised National TB Control Programme; Tuberculosis diagnosis.
Copyright © 2015 Tuberculosis Association of India. Published by Elsevier B.V. All rights reserved.