Inferring Mycobacterium Tuberculosis Drug Resistance and Transmission using Whole-genome Sequencing in a High TB-burden Setting in China.

Objective: China is among the 30 countries with a high burden of tuberculosis (TB) worldwide, and TB remains a public health concern. Kashgar Prefecture in the southern Xinjiang Autonomous Region is considered as one of the highest TB burden regions in China. However, molecular epidemiological studies of Kashgar are lacking.

Methods: A population-based retrospective study was conducted using whole-genome sequencing (WGS) to determine the characteristics of drug resistance and the transmission patterns.

Results: A total of 1,668 isolates collected in 2020 were classified into lineages 2 (46.0%), 3 (27.5%), and 4 (26.5%). The drug resistance rates revealed by WGS showed that the top three drugs in terms of the resistance rate were isoniazid (7.4%, 124/1,668), streptomycin (6.0%, 100/1,668), and rifampicin (3.3%, 55/1,668). The rate of rifampicin resistance was 1.8% (23/1,290) in the new cases and 9.4% (32/340) in the previously treated cases. Known resistance mutations were detected more frequently in lineage 2 strains than in lineage 3 or 4 strains, respectively: 18.6% vs. 8.7 or 9%, P < 0.001. The estimated proportion of recent transmissions was 25.9% (432/1,668). Multivariate logistic analyses indicated that sex, age, occupation, lineage, and drug resistance were the risk factors for recent transmission. Despite the low rate of drug resistance, drug-resistant strains had a higher risk of recent transmission than the susceptible strains (adjusted odds ratio, 1.414; 95% CI, 1.023-1.954; P = 0.036). Among all patients with drug-resistant tuberculosis (DR-TB), 78.4% (171/218) were attributed to the transmission of DR-TB strains.

Conclusion: Our results suggest that drug-resistant strains are more transmissible than susceptible strains and that transmission is the major driving force of the current DR-TB epidemic in Kashgar.