Characterization of pulmonary tuberculosis in high-altitude region using nanopore targeted sequencing

Xizang (formerly known as Tibet in English) has one of the highest tuberculosis (TB) incidence rates in China. The region's extreme altitudes (≥ 3000 m) and hypoxic environment present substantial challenges for conventional diagnostic methods. Additionally, the clinical and biological characteristics of TB at high altitudes remain poorly understood.

TB-seq, a third-generation nanopore-targeted sequencing method, was used to analyze sputum samples from 158 confirmed pulmonary TB patients in Xizang. Bacterial load was quantified, a drug-resistance gene landscape was generated, and these findings were correlated with clinical phenotypes. A matched low-altitude group (< 1000 m) was included to investigate the effects of altitude on Mycobacterium tuberculosis biology.

In Xizang, retreatment cases accounted for the majority of TB patients (58.23%). Type I TB was the most common form (79.75%), while non-type I forms were observed only in retreatment patients (P < 0.01). Bacterial load decreased significantly with increasing age (P < 0.001), was higher in retreatment cases (P = 0.013), and positively correlated with white blood cell and neutrophil counts (P < 0.05). Drug-resistant mutations were identified in 22.78% of patients, primarily as mono-resistance (63.9%), with key resistance-associated genes being rpsL (47.2%), rpoB (38.9%), and katG (33.3%). Compared to low-altitude controls, the high-altitude group had a significantly lower bacterial load (P < 0.01), reduced overall drug resistance (23.7% vs. 38.2%, P < 0.01), no rrs mutations, and a significantly lower pncA mutation rate (P < 0.05).

Tuberculosis in Xizang is marked by a high proportion of retreatment cases, low pathogen burden, and a reduced rate of drug resistance-associated gene mutations. Altitude appears to suppress bacterial quantity and may select for specific resistance mechanisms. These findings support the need for targeted TB control strategies in Xizang and underscore the complex interactions among the environment, the pathogen, and the host.