According to the study, quinolone-resistant strains accounted for more than 85% of S Typhi (the bacteria that causes Typhoid fever) in Bangladesh by the early 2000s, increasing to more than 95% in India, Pakistan and Nepal by 2010.
The mutations causing resistance to azithromycin-a widely used macrolide antibiotic-also have emerged at least seven times in the past 20 years, it said.
Analysis of more than 7,500 S Typhi genomes-mostly from South Asia-showed resistant strains have spread between countries at least 197 times in the past 30 years, according to the largest genome sequencing study of S Typhi that charted the emergence and spread of antibiotic-resistant strains.
The authors of the study performed whole-genome sequencing on 3,489 S Typhi isolates obtained from blood samples collected between 2014 and 2019 from people in Bangladesh, India, Nepal and Pakistan with confirmed cases of typhoid fever.
A collection of 4,169 S Typhi samples isolated from more than 70 countries between 1905 and 2018 was also sequenced and included in the analysis.
While multi-drug resistance to first-line antibiotics has generally declined in South Asia, strains resistant to macrolides and quinolones-two of the most important antibiotics-have risen sharply and spread frequently to other countries, the study said.
“The largest genome analysis of Salmonella enterica serovar Typhi (S Typhi) also reveals that resistant strains-almost all originating in South Asia-have spread to other countries nearly 200 times since 1990,” it said.
Typhoid fever is a global public health concern-there are some 11 million infections and more than 100,000 deaths every year. It is most prevalent in South Asia, accounting for 70% of the global disease burden.
(With inputs from health)