New Delhi: The effectiveness of antibiotics for typhoid fever is threatened by the emergence of resistant strains, according to a large genome sequencing study of the bacteria Salmonella Typhi published in The Lancet Microbe. Typhoid fever causes 11 million infections and more than 100,000 deaths per year. South Asia accounts for 70% of the global disease burden.
Since 2000, multi-drug-resistant (MDR) S Typhi has declined steadily in Bangladesh and India, remained low in Nepal, and increased slightly in Pakistan. However, these are being replaced by strains resistant to other antibiotics, according to the study conducted by researchers from Stanford University, Christian Medical College Vellore, and other institutions. The genome analysis also reveals that resistant strains – almost all originating in South Asia – have spread to other countries 197 times since 1990.
The study sequenced 3,489 S Typhi isolates from 2014-19 from people in Bangladesh, India, Nepal, and Pakistan, and 4,169 samples isolated from over 70 countries during 1905-2018. Strains were classified as MDR if they had genes giving resistance to antibiotics ampicillin, chloramphenicol, and trimethoprim/ sulfamethoxazole.
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“In recent years, we have seen increasingly resistant strains that are threatening to leave us without effective antibiotics against this bacterium. We are already seeing strains for which there is only a single oral antibiotic remaining, termed XDR typhoid. Strains resistant to the antibiotic (azithromycin) have been seen in India, Bangladesh, Nepal, and Pakistan… Evidence to date suggests that much of the drug resistance in typhoid has evolved within India, so we certainly need to be concerned about the appearance of drug resistance in the country,” the study reads.
