Abstract
BackgroundIndigenous typhoid fever was continuing to be identified in Taiwan which has not been endemic for the enteric fever for more than 20 years. The source and transmission by which the local patients acquired typhoid and the population structure of the indigenous typhoid strains remain not well characterized.MethodsDuring 2001 and 2014, non-duplicated clinical Salmonella enterica serovar Typhi isolates in a hospital were analyzed by whole-genome sequencing (WGS) and determined for pulsotypes. Maximum likelihood phylogeny was constructed by nucleotide alterations in core genomes and compared to the framework of global typhoid strains. Potential source and transmission were traced by correlating the phylogeny and the temporal relationship between isolates.ResultsA total of 43 S. Typhi isolates from indigenous cases were analyzed and a majority (39, 90.7%) of them were belonged to six WGS-defined genotypes prevailing mainly in Southeast Asia. Genotype 3.4.0 and a multidrug-resistant type 4.3.1 (also known as pandemic H58 haplotype) were associated respectively with two solitary small-scale outbreaks, implying a transmission mode of importation followed by outbreak. Twelve isolates with nearly identical core genomes were belonged to genotype 3.2.1 but were categorized into three different pulsotypes. The 3.2.1 isolates were identified across 13 years and involved in three clusters and a sporadic case, indicating sustained local transmission of the same strain. The remaining indigenous isolates belonging to three genotypes (2.1, 3.1.2, and 3.0.0) were of substantial genetic diversity and isolated at different time points, indicating independent event of each case.ConclusionsIndigenous typhoid in Taiwan occurred mainly with the forms of small-scale outbreaks or sporadic events likely by contracting imported strains which prevailed in Southeast Asia. Sustained local transmission of certain strain was also evident by WGS analysis, but not by conventional pulsotyping, highlighting the importance of continuing molecular surveillance of typhoid fever with adequate tools in the non-endemic region.
Highlights
Indigenous typhoid fever was continuing to be identified in Taiwan which has not been endemic for the enteric fever for more than 20 years
The detailed origin of isolates, core-genome based phylogenetic relatedness, whole-genome sequencing (WGS)-defined-genotypes, Pulsed-field gel electrophoresis (PFGE) types and the differentially carried resistant genes are shown in Fig. 1 and Additional file 1: Figure S1
Results from the current study demonstrated the continuing occurrences of indigenous typhoid fever with the form of either sporadic events or outbreaks in Taiwan during the past two decades
Summary
Indigenous typhoid fever was continuing to be identified in Taiwan which has not been endemic for the enteric fever for more than 20 years. The source and transmission by which the local patients acquired typhoid and the population structure of the indigenous typhoid strains remain not well characterized. Typhoid fever is a multisystemic illness caused by Salmonella enterica serovar Typhi Human is the only natural host and drinking water and food are the main vehicle for transmission of S. Typhi [1, 2]. The infected cases can transmit bacteriae to other people at their acute illness and 1 to 5% of the cases recovered from typhoid fever become carriers [3].
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