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The bacteria that cause typhoid fever are becoming increasingly resistant to some of the most important antibiotics for human health, according to a study published in “The Lancet Microbe.” The analysis of the largest genome 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.
Typhoid fever is a global public health problem, causing 11 million infections and more than 100,000 deaths a year. While it is most prevalent in South Asia, which accounts for 70% of the global disease burden, it also has a significant impact in sub-Saharan Africa, Southeast Asia and Oceania, highlighting the need for a global response.
Antibiotics can be used to successfully treat typhoid infections, but their effectiveness is threatened by the emergence of resistant strains of S. Typhi. Until now, analysis of the rise and spread of resistant S. Typhi has been limited, with most studies based on small sample sizes.
The authors performed whole genome sequencing on 3,489 S. Typhi samples 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.
Resistance-conferring genes in the 7,658 sequenced genomes were identified using genetic databases. Strains were classified as multidrug-resistant (MDR) if they contained genes that confer resistance to the classic first-line antibiotics ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole.
They also tracked the presence of genes that confer resistance to macrolides and quinolones, which are among the most important antibiotics for human health.
The analysis shows that resistant strains of S. Typhi have spread between countries at least 197 times since 1990. While these strains occurred most frequently in South Asia and from South Asia to Southeast Asia, the eastern and southern Africa, have also been reported in the UK, USA and Canada.
The findings add to recent evidence of the rapid rise and spread of S. Typhi strains resistant to cephalosporins third generation, another class of antibiotics critically important to human health.
“The speed at which highly resistant strains of S. Typhi have emerged and spread in recent years is a real cause for concern and highlights the need to urgently scale up prevention.” measures, particularly in high-risk countries. At the same time, the fact that resistant strains of S. Typhi have spread internationally so many times also underscores the need to consider typhoid control and antibiotic resistance in general as a global rather than a local problem.” warns lead author Jason Andrews of Stanford University.
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