Chasing down the acid-fast bacilli during treatment: need better yardsticks.

I read with great interest the article by Chien et al 1 in a recent issue of CHEST (June 2013) wherein the authors reported the signifi cance of smear positivity of acid-fast bacillus at the end of the fi fth month of treatment in patients with non-multidrug-resistant (MDR) TB. The principal query in reference to this study arises with regard to its clinical and practical implication in the fi eld setting. The conclusions of this research are probably of more interest in countries with a low prevalence of TB and not of practical use in countries with a high prevalence of TB. Countries with a high burden of TB are still struggling to pick up MDR TB cases at an early phase of treatment because of a lack of adequate resources (ie, widespread availability of drug culture and sensitivity methods). 2 Hence, by carrying out drug susceptibility testing at the start of treatment (ie, ruling out MDR TB at the outset), the practical application of this study is questionable. Second, excluding drug-resistant bacilli right at the start of treatment creates an obvious bias toward isolation of nontubercular mycobacteria and nonviable bacilli as the reason for persistent sputum positivity later during the course of treatment. The SCOR index (smear grading  3 1 at the fi fth month [S], no sputum culture conversion at the second month [C], lack of direct observation strategy [O], and no radiographic improvement at the fi fth month [R]) appears to be a useful tool for monitoring treatment response because it does not require extra equipment or investment. A modifi ed version of the SCOR index can be used, whereby the sputum smear for acid-fast bacilli status at 2 or 3 months can be taken instead of the fi rst two indicators. This indicator can be used as a screening tool. Patients with a higher such index at 2 or 3 months of antitubercular treatment can be subjected to drug susceptibility testing because of an increased probability of picking up drug-resistant bacilli at an early stage of treatment . This would surely warrant a large-scale study for defi nitive conclusions.