The epidemiology, pathogenesis, transmission, diagnosis, and management of multidrug-resistant, extensively drug-resistant, and incurable tuberculosis

The available information on the epidemic of drug-resistant tuberculosis in China is based on local or regional surveys. In 2007, we carried out a national survey of drug-resistant tuberculosis in China. We estimated the proportion of tuberculosis cases in China that were resistant to drugs by means of cluster-randomized sampling of tuberculosis cases in the public health system and testing for resistance to the first-line antituberculosis drugs isoniazid, rifampin, ethambutol, and streptomycin and the second-line drugs ofloxacin and kanamycin. We used the results from this survey and published estimates of the incidence of tuberculosis to estimate the incidence of drug-resistant tuberculosis. Information from patient interviews was used to identify factors linked to drug resistance. Among 3037 patients with new cases of tuberculosis and 892 with previously treated cases, 5.7% (95% confidence interval [CI], 4.5 to 7.0) and 25.6% (95% CI, 21.5 to 29.8), respectively, had multidrug-resistant (MDR) tuberculosis (defined as disease that was resistant to at least isoniazid and rifampin). Among all patients with tuberculosis, approximately 1 of 4 had disease that was resistant to isoniazid, rifampin, or both, and 1 of 10 had MDR tuberculosis. Approximately 8% of the patients with MDR tuberculosis had extensively drug-resistant (XDR) tuberculosis (defined as disease that was resistant to at least isoniazid, rifampin, ofloxacin, and kanamycin). In 2007, there were 110,000 incident cases (95% CI, 97,000 to 130,000) of MDR tuberculosis and 8200 incident cases (95% CI, 7200 to 9700) of XDR tuberculosis. Most cases of MDR and XDR tuberculosis resulted from primary transmission. Patients with multiple previous treatments who had received their last treatment in a tuberculosis hospital had the highest risk of MDR tuberculosis (adjusted odds ratio, 13.3; 95% CI, 3.9 to 46.0). Among 226 previously treated patients with MDR tuberculosis, 43.8% had not completed their last treatment; most had been treated in the hospital system. Among those who had completed treatment, tuberculosis developed again in most of the patients after their treatment in the public health system. China has a serious epidemic of drug-resistant tuberculosis. MDR tuberculosis is linked to inadequate treatment in both the public health system and the hospital system, especially tuberculosis hospitals; however, primary transmission accounts for most cases. (Funded by the Chinese Ministry of Health.).

Mycobacterium tuberculosis strains of the Beijing lineage are globally distributed and are associated with the massive spread of multidrug-resistant (MDR) tuberculosis in Eurasia. Here we reconstructed the biogeographical structure and evolutionary history of this lineage by genetic analysis of 4,987 isolates from 99 countries and whole-genome sequencing of 110 representative isolates. We show that this lineage initially originated in the Far East, from where it radiated worldwide in several waves. We detected successive increases in population size for this pathogen over the last 200 years, practically coinciding with the Industrial Revolution, the First World War and HIV epidemics. Two MDR clones of this lineage started to spread throughout central Asia and Russia concomitantly with the collapse of the public health system in the former Soviet Union. Mutations identified in genes putatively under positive selection and associated with virulence might have favored the expansion of the most successful branches of the lineage.

The frequency and rates of ascent and dissemination of antibiotic resistance in bacterial populations are anticipated to be directly related to the volume of antibiotic use and inversely related to the cost that resistance imposes on the fitness of bacteria. The data available from recent laboratory studies suggest that most, but not all, resistance-determining mutations and accessory elements engender some fitness cost, but those costs are likely to be ameliorated by subsequent evolution.