New research: Study flags emergence of drug-resistant typhoid strains

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.

“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,” lead author Dr Jason Andrews of Stanford University told The Indian Express.

India’s Health Ministry is considering introducing new typhoid conjugate vaccines into the national immunisation program. Two WHO-prequalified vaccines have been developed in India (by Bharat Biotech and Biological E). Study author Prof Jacob John of CMC Vellore said surveillance at 18 Indian sites during 2016-20 found typhoid was as common as it was two decades ago, especially in urban areas. “Complications and deaths are not common… However if transmission still prevails and resistance develops to commonly used antibiotics, then it is likely that there will be an upsurge in severe disease,” Prof John told The Indian Express.