Strains were classified as multidrug-resistant (MDR) if they contained genes giving resistance to the classic first-line antibiotics, ampicillin, chloramphenicol and trimethoprim/sulfamethoxazole.
The authors also traced the presence of genes conferring resistance to macrolides and quinolones, which are among the most important antibiotics for human health.
The analysis shows that resistant strains of S. Typhi have spread between countries at least 197 times since 1990.
Although these strains occur most commonly in South Asia and South Asia to Southeast Asia, East and Southern Africa, they have also been reported in the UK, USA and in Canada, the researchers said.
Since 2000, MDR S. Typhi has declined steadily in Bangladesh and India, and remained low in Nepal, although it has increased slightly in Pakistan.
However, these are being replaced by strains resistant to other antibiotics, they said. For example, genetic mutations giving resistance to quinolones have appeared and spread at least 94 times since 1990, almost all of them (97%) coming from South Asia.
The study found that quinolone resistant strains accounted for over 85% of S. Typhi in Bangladesh in the early 2000s, rising to over 95% in India, Pakistan and Nepal in 2010.
Pediatrics, when do you need antibiotics?
Quebec parents struggle to get antibiotics for their children amid national shortage
Shortage of antibiotics for children in Quebec