Phylogenetic Analysis of an Unusual Increase in Salmonella enterica serovar Paratyphi A Infection among Travelers Returning from Myanmar

BACKGROUND: The proportion of enteric fever cases caused by Salmonella enterica subspecies enterica serovar Paratyphi A (S. Paratyphi A) has recently been increasing in Asian counties, which is a public health concern. In 2015, an unusual increase in S. Paratyphi A infection among Japanese travelers returning from Myanmar was noted, while there is little information on this uptrend in Myanmar. METHODS: Isolates from travelers who returned with enteric fever from 2005 to 2015 were analyzed in order to determine country-specific notification rates (epidemiological investigation). The notification rate was defined as cases returning from each country per 100,000 Japanese travelers who visited to the country. S. Paratyphi A isolates collected from 2001 to 2015 were analyzed by whole-genome sequencing (microbiological investigation). RESULTS: Yearly notification trends indicated that enteric fever was potentially endemic to Myanmar (5–16 cases/100,000 travelers); the trends were similar to those observed in India (4–21 cases/100,000 travelers). A rapid increase in S. Paratyphi A infection occurred from 2012–2014 (2–4 cases/100,000 travelers) to 2015 (13 cases/100,000 travelers). A phylogenetic tree, constructed based on analysis of 105 S. Paratyphi A isolates (33 and 30 related to Myanmar and Cambodia, and 42 controls), revealed that most Myanmar- and Cambodia-related isolates formed clusters in the same lineage (Figure 1). Additionally, Myanmar-related isolates from 2015 harbored identical phage type 1 and were genetically closely related [each isolates had 0–10 single-nucleotide polymorphisms (SNPs), mostly within 0–7 SNPs] (Figure 2), yielding a wider SNP range than outbreak-associated isolates from Cambodia in 2013 (within a SNP distance of 0–6). CONCLUSION: Epidemiological trends and molecular subtyping suggested a possible outbreak of S. Paratyphi A infection occurred in Myanmar in 2015. The recent uptrend of S. Paratyphi Ainfection in Myanmar is important for travelers and clinicians since infection cannot be prevented by typhoid vaccination. Figure 1. Polygenetic tree of 105 S. Paratyphi A isolates Figure 2. SNP analyses of S. Paratyphi A isolates from Myanmar in 2015 (A) and Cambodia in 2013 (B). DISCLOSURES: All authors: No reported disclosures.