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Typhoid fever causing bacteria have become more resistant to antibiotics over the past 30 years, study finds

Published: 22 Jun 2022 03:16 GMT

Over the past 30 years, the bacterium that causes typhoid fever has become more resistant to some of the most commonly used antibiotics for human health, according to a study published June 21 in the journal The Lancet Microbe.

The findings obtained by an international group of scientists following genomic analysis of ‘Salmonella enterica serovar typhi’ (abbreviated as S.Typhi) also reveal that resistant strains have spread at least 197 times between different countries since 1990. Most of the strains were located in South Asia, as well as in East and Southern Africa, the UK, USA and Canada.

Although antibiotic resistance has declined in South Asia overall, strains resistant to drugs such as macrolides and quinolones (both among the most critical antibiotics) have increased considerably, spreading to other countries.

“The speed with 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, especially in the countries most at risk,” stressed Jason Andrews, lead author of the study, from Stanford University (USA).

“At the same time, the fact that resistant strains have spread internationally so many times also underlines the need to consider the control of typhoid fever, and antibiotic resistance more generally, as a global and not a local problem,” he summarized, as quoted by the Medicalxpress portal.

As part of the work, the specialists carried out the complete genomic sequencing of 3,489 strains identified in blood samples taken between 2014 and 2019 from patients confirmed with the disease from Bangladesh, India, Nepal and Pakistan. Another 4,169 samples from more than 70 countries taken between 1905 and 2018 were sequenced and then added to the analysis.

The results showed that genetic mutations that develop resistance to quinolones have spread at least 94 times since 1990, with 97% of the cases occurring in South Asia. Thus, quinolone-resistant strains accounted for more than 85 % of S.Typhi in Bangladesh in early 2000, while the rate rose to more than 95 % in India, Pakistan and Nepal by 2010.

Moreover, mutations that develop resistance to azithromycin (a macrolide antibiotic), have been reported at least seven times in the last two decades.

According to World Health Organization (OMS) estimates, between 11 and 21 million people contract typhoid fever each year. Of these, between 128,000 and 161,000 die.
Among the groups most at risk are communities without access to safe drinking water or adequate sanitation systems. “Typhoid fever can be treated with antibiotics, although increasing resistance to different types of antibiotics makes treatment more complicated. Even after the disappearance of symptoms, the sick person can remain a carrier of the bacteria and transmit it through feces,” the ONU institution stresses.

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