Resistance to Second-Line Antituberculosis Drugs and Delay in Drug Susceptibility Testing among Multidrug-Resistant Tuberculosis Patients in Shanghai.

Introduction. Second-line antituberculosis drugs (SLDs) are used for treating multidrug-resistant tuberculosis (MDR-TB). Prolonged delays before confirming MDR-TB with drug susceptibility testing (DST) could result in transmission of drug-resistant strains and inappropriate use of SLDs, thereby increasing the risk of resistance to SLDs. This study investigated the diagnostic delay in DST and prevalence of baseline SLD resistance in Shanghai and described the distribution of SLD resistance with varied delays to DST. Methods. All registered patients from 2011 to 2013 in Shanghai were enrolled. Susceptibility to ofloxacin, amikacin, kanamycin, and capreomycin was tested. Total delay in DST completion was measured from the onset of symptoms to reporting DST results. Results. Resistance to SLDs was tested in 217 of the 276 MDR-TB strains, with 118 (54.4%) being resistant to at least one of the four SLDs. The median total delay in DST was 136 days. Patients with delay longer than median days were roughly twice more likely to have resistance to at least one SLD (OR 2.22, 95% CI 1.19-4.11). Conclusions. During prolonged delay in DST, primary and acquired resistance to SLDs might occur more frequently. Rapid diagnosis of MDR-TB, improved nosocomial infection controls, and regulated treatment are imperative to prevent SLD resistance.