Prolonged Outbreak of Multidrug-Resistant Shigella sonnei Harboring in Victoria, Australia.

In Australia, cases of shigellosis usually occur in returned travelers from regions of shigellosis endemicity or in men who have sex with men. Resistance to multiple antibiotics has significantly increased in isolates and represents a significant public health concern. We investigate an outbreak of multidrug-resistant in Victoria, Australia. We undertook whole-genome sequencing of 54 extended-spectrum-beta-lactamase (ESBL)-producing isolates received at the Microbiological Diagnostic Unit Public Health Laboratory between January 2019 and March 2020. The population structure and antimicrobial resistance profiles were identified by genomic analyses, with 73 previously characterized Australian isolates providing context. Epidemiological data, including age and sex of the shigellosis cases, were also collected. There was a significant increase in cases of ESBL from July 2019. Most of the ESBL isolates (65%) fell within a single cluster that was predominantly comprised of male cases that were characterized by the presence of the gene conferring resistance to extended-spectrum cephalosporins. These isolates were also multidrug resistant, including resistance to azithromycin and co-trimoxazole and reduced susceptibility to ciprofloxacin. Our data uncovered a prolonged clonal outbreak of ESBL infection that was likely first introduced by returned travelers and has subsequently been circulating locally in Australia. The emergence of a local outbreak of ESBL with a multidrug-resistant profile, including reduced susceptibility to ciprofloxacin, represents a significant public health threat.