The rise in domestic shigellosis and the genomic characteristics of
Shigella
clones linked to men who have sex with men in Taiwan, 2015‒2022
Authors: Liao Ying-Shu , Chen Bo-Han , Hong Yu-Ping , Wang You-Wun , Teng Ru-Hsiou , Liang Shiu-Yun , Chang Jui-Hsien , Tsao Chi-Sen , Wei Hsiao Lun , Chiou Chien-Shun 
Published: February 2025

ABSTRACT

Since 2015, Taiwan has experienced a notable rise in domestic shigellosis cases, particularly among young adult males. In this study, we aimed to investigate this epidemiological trend through demographic analysis and genomic characterization of bacterial isolates. We analyzed demographic data on shigellosis cases from 2003–2014 to 2015–2022. For cases from 2015–2022, we conducted genomic analyses of
Shigella
isolates using pulsed-field gel electrophoresis (PFGE) and whole-genome sequencing (WGS). Antimicrobial resistance and plasmid profiles were examined to identify genetic determinants of resistance. From 2015 to 2022, there was a noticeable demographic shift in domestic shigellosis cases from females to males and children to young adults. This trend was driven by three multidrug-resistant
Shigella
clones associated with men who have sex with men (MSM): ciprofloxacin-resistant
S. sonnei
(CipR_SSIII), azithromycin-resistant
S. flexneri
3a (AziR_SF3), and ciprofloxacin-resistant
S. flexneri
2a (CipR_SF2). The CipR_SF2 clone has become the most prevalent since 2018, responsible for 84.9% of cases in 2021. Genomic analysis revealed that CipR_SF2 isolates are genetically distinct from those involved in MSM-related outbreaks in other countries. These MSM-associated clones showed significantly higher resistance to azithromycin, extended-spectrum cephalosporins (ESCs), and ciprofloxacin. Additionally, 14 extensively drug-resistant isolates were identified, carrying resistance genes for azithromycin and ESCs on IncFII or IncB/O/K/Z plasmids. Our findings indicate that the increase in domestic shigellosis cases in Taiwan from 2015 to 2022 is primarily attributed to the spread of highly resistant MSM-associated
Shigella
clones.

IMPORTANCE
The rise of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Shigella strains poses a growing global health threat, particularly among high-risk groups such as men who have sex with men (MSM). This study highlights the increasing prevalence of domestic shigellosis in Taiwan from 2015 to 2022, driven by the emergence of three MDR Shigella clones. These MSM-associated clones exhibit significantly higher resistance to azithromycin, extended-spectrum cephalosporins (ESCs), and ciprofloxacin compared to non-MSM-associated clones. Additionally, 14 extensively drug-resistant isolates were identified, carrying resistance genes for azithromycin and ESCs on IncFII or IncB/O/K/Z plasmids. Genomic analysis reveals that ciprofloxacin-resistant Shigella flexneri 2a (CipR_SF2) has become the most dominant clone, responsible for the majority of shigellosis cases since 2018, and is genetically distinct from strains observed in MSM-related outbreaks in other countries. By elucidating these clones’ genetic characteristics and epidemiological trends, this research offers essential data for public health surveillance, helping to inform strategies for controlling the spread of MDR and XDR Shigella infections.