Paratyphoid Fever and the Genomics of Salmonella enterica Serovar Paratyphi A in Taiwan
Listed in
This article is not in any list yet, why not save it to one of your lists.Abstract
Background
Salmonella enterica serovar Paratyphi A has emerged as a significant global health concern due to the progressive development of antimicrobial resistance and its broader geographic distribution. In Taiwan, paratyphoid fever was historically rare and predominantly associated with imported cases. Since 2022, however, a marked increase in domestically acquired infections has been observed, prompting investigations into their origin and likely route of introduction.
Methods
We analyzed surveillance data on 223 patients with paratyphoid fever reported in Taiwan between 2001 and 2024. Whole-genome sequencing and antimicrobial susceptibility testing were performed on 88 S. Paratyphi A isolates obtained from both imported and domestically acquired infections from 2007 to 2024. Phylogenetic analysis and genotyping were conducted to assess genetic relatedness and to trace potential sources of introduction by comparing them with global isolates.
Results
Although 55.2% of paratyphoid fever infections were imported, domestically acquired infections became predominant after 2022. Most isolates (76.1%) were resistant to nalidixic acid and nonsusceptible to ciprofloxacin due to gyrA mutations at codon 83 (S83F or S83Y). The majority of domestic isolates were classified as ST129 and paratype 2.4 and showed close genetic relatedness to strains from Indonesia. Of the 31 domestic isolates collected between 2022 and 2024, 30 clustered with Indonesian strains, and 28 exhibited very limited genetic divergence, suggesting a likely common source of infection.
Conclusions
S. Paratyphi A isolates recovered from recent domestically acquired infections in Taiwan are genetically related to strains from Indonesia. The high rate of ciprofloxacin nonsusceptibility, driven by gyrA mutations, highlights the need for ongoing resistance monitoring, while the preserved susceptibility to traditional first-line agents supports their continued use in treatment. Genomic surveillance proved effective for source tracking and guiding public health interventions.
Author summary
Paratyphoid fever, caused by Salmonella enterica serovar Paratyphi A, is typically associated with endemic regions in South and Southeast Asia. In Taiwan, the disease has historically been rare and primarily linked to imported cases. However, since 2022, the number of locally acquired infections has increased. We analyzed 88 S. Paratyphi A isolates collected in Taiwan between 2007 and 2024 using whole-genome sequencing and antimicrobial susceptibility testing. While 76.1% of isolates were resistant to nalidixic acid and exhibited reduced susceptibility to ciprofloxacin, these phenotypes were associated with gyrA mutations at codon 83, which are known to impair the efficacy of fluoroquinolones. Importantly, all isolates remained susceptible to 13 other tested antimicrobials, including older drugs such as ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. Phylogenetic analysis showed that most domestic isolates belonged to the same genetic lineage as strains from Indonesia. Notably, 28 of 30 isolates collected from domestic cases between 2022 and 2024 exhibited near-identical genetic profiles, despite patients having no epidemiological links. This suggests that the infections likely originated from a common external source, such as contaminated imported food or an environmental reservoir, rather than through sustained local transmission. Our study highlights the value of genomic surveillance in tracing infection sources and provides evidence to support targeted public health interventions and treatment strategies that preserve the use of traditional first-line antibiotics where susceptibility remains high.
