A comparative study of Conventional methods and GeneXpert Mycobacterium tuberculosis Rifampicin (MTB/RIF) assay for diagnosis of childhood pulmonary tuberculosis

Background Diagnosis of childhood TB (tuberculosis) is challenging because its symptoms resemble other diseases, very few (less than five) mycobacteria are capable of causing the disease and children do not or rarely expectorate. These peculiar attributes make childhood TB different from adult TB but it is still not being dealt differently from adult TB .Despite evidences from national, international data and WHO recommendation for use of Gene expert/TB/RIF assay, decision to start the treatment is based mostly on Chest X ray, tuberculin skin test, history of contact and clinical sign and symptoms .Therefore, we planned this study to find best available choices of diagnostic tests for early case detection of childhood TB particularly MDR TB Methods: This comparative analytical study of 15 months was done at PHRC, SRCCH, NICH and Provincial TB Lab Ojha Institute of chest diseases Karachi. Our study population comprised of 143 probable cases of pulmonary TB below the age of 15 years. After taking written consent from parent/guardian, a Performa was filled with contact no, address, clinical history, scoring chart and diagnostic tests suggested by attending clinician. ZN staining for smear microscopy GeneXpert Mycobacterium tuberculosis Rifampicin (Xpert MTB/RIF) assay, Culture on Lowenstein–Jensen (L.J) media and Mycobacterium Growth Indicator Tube (MGIT) was done for every sample according to standard operating procedures of WHO and results were entered and analyzed on SPSS statistical package for social sciences. Results Out of 143 samples 7 (5%) were positive for MTB via Xpert MTB/RIF assay while 3(2.09) were positive through AFB microscopy, LJ culture and MGIT. When compared with gold standard blood culture sensitivity and negative predictive value of Xpert MTB/RIF were 100% and 97.14% while specificity and positive predictive value were 97.14% and 43% respectively. Conclusion Xpert MTB/RIF is a rapid test that can aid in timely diagnosis of peds TB, facilitating the timely treatment. However, specificity and PPV need to be taken into account. Key words: AFB microscopy, LJ and MGIT, Xpert MTB/RIF, Peds TB.