Study: Drug-Resistant Typhoid May Become Epidemic

Authors of a new study say they have determined how Salmonella typhi, a multidrug-resistant strain of typhoid, has surfaced and spread throughout the past 30 years, reaching a stage that may now represent an epidemic.

Seeking to understand the emergence and pervasiveness of these antibiotic-resistant typhoid strains, a team including researchers from the University of Melbourne and the Wellcome Trust Sanger Institute collected 1,832 samples of S. typhi from 63 countries between 1992 and 2013, sequencing the genomes of each one.
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Overall, the investigators found that 47% of these samples belonged to an antibiotic-resistant strain of typhoid known as H58, which the authors say they believe is a key driver of antibiotic-resistant typhoid. According to the authors, this strain—which first emerged in South Asia between 25 and 30 years ago—has evolved in that time by obtaining new gene mutations as it makes its way through areas exposed to new antibiotics.

The researchers also found evidence of an ongoing H58 epidemic throughout Africa, which they say is supported by the available epidemiological data, including a growing number of reports indicating multidrug-resistant typhoid in Africa. This finding underscores the need to control antibiotic prescription practices in the region, the authors note.

This study “highlights the global public health threat caused by multi-drug resistant typhoid,” says Vanessa Wong, an infectious diseases specialist at the Wellcome Trust Sanger Institute, and lead author of the study.  

“It allows us to better understand how anti-microbial resistance emerges and spreads globally,” says Wong, “and thus will enable us to develop effective strategies to control typhoid.”

For example, she says, the findings can help guide management of the disease and aid appropriate antibiotic choice, by providing “useful information to primary care practitioners in typhoid- endemic countries, [regarding] whether they have multidrug-resistant typhoid circulating in their region.”

The study also emphasizes the need to recommend receiving the typhoid vaccine to individuals traveling in parts of the world where the disease is endemic, she says, “as the vaccine is effective against all strains of typhoid, even those that have become antibiotic-resistant.”

—Mark McGraw

Reference

Wong V, Baker S, et al. Phylogeographical analysis of the dominant multidrug-resistant H58 clade of Salmonella Typhi identifies inter- and intracontinental transmission events. Nature Genetics. 2015.