# Genomic and epidemiological characteristics of Shigella boydii in Australia, 1991–2022

## TL;DR

This study analyzed S. boydii infections in Australia and globally from 1991 to 2022, revealing increasing cases, overseas acquisition, and antimicrobial resistance patterns.

## Contribution

The largest genomic analysis of S. boydii to date, combining epidemiological and genomic data to reveal global population structure and AMR trends.

## Key findings

- 54% of S. boydii cases in Australia were acquired overseas, mainly from South-East Asia.
- Genomic analysis identified five global S. boydii lineages, with Australian isolates predominantly in Lineage 3.
- Over 60% of isolates were multi-drug-resistant, with emerging resistance to ciprofloxacin and other clinically relevant antimicrobials.

## Abstract

Shigellosis is a leading cause of diarrheal mortality worldwide. Shigella boydii is one of four Shigella species that contributes to this burden, however studies on S. boydii are limited. Here we combined epidemiological and genomic data to better understand S. boydii circulating both in Australia and globally. Between 1991 and 2019, there were 294 cases of S. boydii infections notified to the National Notifiable Diseases Surveillance System by Australian states and territories, with an increasing trend in notifications observed from 2013. Of cases whose place of acquisition was known, 54% (111/206) were acquired overseas, mainly from South-East Asia (57%; 63/111). Our genomic analysis included 250 S. boydii isolates: 44 from Victoria, Australia spanning 22 years (2001–2022) and 206 international isolates spanning 91 years (1930–2020). Phylogenomic analyses identified five major S. boydii phylogenetic lineages circulating globally. The Australian isolates were distributed across all five lineages, but the highest proportion was in Lineage 3. Antimicrobial resistance was common in both international and Australian isolates with > 60% of isolates classified as multi-drug-resistant. Resistance to the main clinically relevant antimicrobials was rare in S. boydii. Ciprofloxacin resistance was detected in seven S. boydii, however reduced susceptibility to ciprofloxacin was detected in 56 isolates and found in both Australian and international data. Importantly, resistance mechanisms to third-generation cephalosporins and macrolides were also detected. This study is the largest genomic analysis of S. boydii to date, providing insights into the population structure, epidemiology and emerging AMR threats in this neglected Shigella species.