Drug-resistance characteristics, genetic diversity, and transmission dynamics of multidrug-resistant or rifampicin-resistant Mycobacterium tuberculosis from 2019 to 2021 in Sichuan, China.

Background: Multidrug- or rifampicin-resistant tuberculosis (TB; MDR/RR-TB) is a significant public health threat. However, the mechanisms involved in its transmission in Sichuan, China are unclear. To provide a scientific basis for MDR/RR-TB control and prevention, we investigated the drug-resistance characteristics, genetic diversity, and transmission dynamics and analyzed the demographic and clinical characteristics of patients to identify risk factors for the acquisition of MDR/RR-TB in Sichuan, Western China.

Methods: Whole-genome sequencing was performed using a sample comprised of all MDR/RR-TB strains isolated from patients with pulmonary TB (≥ 15 years) at the 22 surveillance sites in Sichuan province between January 2019 and December 2021, to analyze genotypic drug resistance and genetic diversity. Moreover, we performed statistical analyses of the epidemiological characteristics and risk factors associated with the transmission dynamics of MDR/RR-TB.

Results: The final analysis included 278 MDR/RR TB strains. Lineage 2.2, the major sub-lineage, accounted for 82.01% (228/278) of isolates, followed by lineage 4.5 (9.72%, 27/278), lineage 4.4 (6.83%, 19/278), and lineage 4.2 (1.44%, 4/278). The drug resistance rates, ranging from high to low, were as follows: isoniazid (229 [82.37%]), streptomycin (177 [63.67%]), ethambutol (144 [51.80%]), pyrazinamide (PZA, 119 [42.81%]), fluoroquinolones (FQs, 93 [33.45%]). Further, the clofazimine, bedaquiline, and delamanid resistance rates were 2.88, 2.88, and 1.04%, respectively. The gene composition cluster rate was 32.37% (90/278). In addition, 83.81% (233/278) of MDR/RR-TB cases were determined to be likely caused by transmission. Finally, patients infected with lineage two strains and strains with the KatG S315T amino acid substitution presented a higher risk of MDR/RR-TB transmission.

Conclusion: Transmission plays a significant role in the MDR/RR-TB burden in Sichuan province, and lineage 2 strains and strains harboring KatG S315T have a high probability of transmission. Further, high levels of FQ and PZA drug resistance suggest an urgent need for drug susceptibility testing prior to designing therapeutic regimens. New anti-TB drugs need to be used standardly and TB strains should be regularly monitored for resistance to these drugs.