Does my patient have multidrug-resistant tuberculosis?

After how long in tuberculosis (TB) treatment can I expected my patient to have negative smear or culture results? This is a common concern of clinicians throughout the world. One worry is about the infectiousness of the patient with TB. A patient who is smear negative can be expected to be less infectious than one who is smear positive, and this may indicate that he or she is safe to reenter the home and society. However, an even greater worry is about drug resistance, especially in an era when multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains are increasingly common. In developing countries, most TB is still treated empirically, without the benefit of drug susceptibility tests (DSTs). In these settings, failure to respond to first-line TB drugs is the only way to identify patients at risk for MDR TB. The question posed is a crucial one when evaluating a patient who is still smear positive after completing 2 months of treatment. Is the patient just a slow converter or does the patient have MDR TB? A study by Fitzwater et al [1] published