Eleven-year experience on anti-TB drugs direct susceptibility testing from Siriraj Hospital, Thailand

The early detection of drug-resistant tuberculosis (TB) strains is of utmost importance for patient management and effective TB control programs. This study aimed to demonstrate the performance of direct drug susceptibility testing (DST) performed in our laboratory in the past 11 years. The direct DST was performed on Middlebrook 7H10 medium using isoniazid (INH) and rifampicin (RIF), and the results were compared with those obtained from indirect DST (gold standard). The direct DST was performed with 15,598 smear-positive sputum samples, of which 11,284 (72%) yielded reportable results. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated and revealed 89%, 99%, 95%, and 99%, respectively, for RIF and 90%, 98%, 93%, and 97%, respectively, for INH. Direct DST results could be reported within 1 month after sample processing. This method was also shown to be suitable for use in resource-limited countries, particularly in settings with high numbers of TB cases.