Epidemiologic and genomic investigations of an unusual increase in Salmonella enterica serovar Paratyphi A infection among travelers returning from Myanmar in 2015

Objectives: An unusual increase in Salmonella enterica serovar Paratyphi A infection rate in Japanese travelers returning from Myanmar was observed in 2015. Methods: We analyzed epidemiologic data of returned travelers with enteric fever from 2005-2019. We also analyzed 193 Salmonella Paratyphi A isolates, including 121 isolates with published genomes. Results: Annual notification trends showed a rapid increase in Salmonella Paratyphi A infection in travelers returning from Myanmar in 2015: 2-4 cases/100,0 00 travelers in 2012-2014 and 13 cases/100,0 00 travelers in 2015 (P <0.001). The genomic analyses revealed that 11 Myanmar-related isolates in 2015 formed a tight cluster in clade 3 with a single nucleotide variant (SNV) distance of 0-11 (primarily 0-7), yielding a wider SNV range than outbreak-associated isolates from Cambodia in 2013 (0-6 SNVs) or China in 2010 (0-5 SNVs). Although all Cambodia-related isolates in 2013 harbored the wild-type gyrA sequence, all Myanmar-related isolates in 2015 had a single, identical mutation (Ser83Phe) in the gyrA gene. Conclusion: The epidemiologic and molecular investigations suggested an increase in the infection rate with genetically closely related Salmonella Paratyphi A in travelers returning from Myanmar in 2015. Careful monitoring of the infection in Myanmar as an endemic country is warranted, considering the resumption of cross-border travel during the COVID-19 pandemic. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Automated summary

In 2015, there was an unusual increase in Salmonella Paratyphi A infection rate in Japanese travelers returning from Myanmar. Epidemiologic and molecular investigations revealed a close genetic relationship between the infections.