Typhoid bacteria increasingly resistant to key drugs, says Lancet study, flags ‘India risk’

New Delhi: Bacteria that cause typhoid fever are becoming increasingly resistant to some of the most commonly used antibiotics, according to a. study published in The lancet microbe news Wednesday.

Such strains, which showed some degree of drug resistance, have become increasingly common in countries like India over the past 30 years, the study by an international team of researchers, including those from Stanford University in the US, found.

Typhoid fever, which spreads through contaminated water or food, causes 11 million infections (110 lakh) and over 100,000 deaths per year, with South Asia accounting for 70 percent of the global burden of disease. While antibiotics can be used to successfully treat typhoid fever infections, their effectiveness is threatened by the emergence of resistant strains of the bacteria, Salmonella typhi (s† typhi).

The researchers performed whole genome sequencing at 3,489 s† Typhi samples collected from typhoid patients in India, Bangladesh, Nepal and Pakistan between 2014 and 2019. They also analyzed sequence data from 4,169 additional samples from s† Typhi was isolated from more than 70 countries between 1905 and 2018.

They found that drug-resistant strains — almost all of them native to South Asia — have spread to other countries in nearly 200 cases since 1990.

“The rate at which highly resistant strains of s† Typhi that has emerged and spread in recent years is a real cause for concern and emphasizes the need to urgently expand prevention measures, especially in countries with the highest risk,” said Jason Andrews, a researcher at the United Nations. Stanford University and the study’s lead author, in a statement.

“At the same time, the fact that resistant strains of s† Typhi that has so often spread internationally also underscores the need to see typhoid control and antibiotic resistance more broadly as a global rather than a local problem,” he added.

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Multi-resistant strains

Researchers identified as many as 7,658 samples with genetic variations that conferred drug resistance s† Typhi bacteria.

The strains were classified as multidrug resistant (MDR) if they were found to contain genes that rendered them resistant to multiple antibiotics such as ampicillin, chloramphenicol and trimethoprim/sulfamethoxazole.

Mutations that made bacteria resistant to azithromycin — a commonly used antibiotic — were found at least seven times in the past 20 years, according to the study.

In addition, the researchers were able to identify genes in s† Typhi samples that make bacteria resistant to macrolides and quinolones, which are among the most common critically important antimicrobials.

The study showed that drug-resistant s† Typhi strains have spread between countries in at least 197 cases since 1990.

While most of these strains were found in South and Southeast Asia and East and South Africa, some have also been reported from the UK, US and Canada.

Since 2000, multi-resistant strains of s† Typhi has steadily declined in Bangladesh and India.

However, these are now being replaced by strains that are resistant to other antibiotics.

For example, gene mutations that make strains resistant to quinolones — a large group of antibiotics that directly kill bacterial cells — have spread at least 94 times since 1990, with nearly 97 percent of these strains being traced to South Asia. Quinolone-resistant strains accounted for more than 85 percent of the S. Typhi samples found in Bangladesh by the early 2000s. In 2010, these strains accounted for more than 95 percent of isolated samples in India, Pakistan and Nepal.

(Edited by Amrtansh Arora)

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