The following is a summary of “Genomic reconstruction and directed interventions in a multidrug-resistant Shigellosis outbreak in Seattle, WA, USA: a genomic surveillance study,” published in the June 2023 issue of the Infectious Diseases by Tansarli et al.

In urban contexts, Shigella spp has been linked to community-wide outbreaks. The researchers analyzed a sustained outbreak of shigellosis in Seattle, Washington, USA, to determine its origins and mechanisms of antimicrobial resistance, define ongoing transmission patterns, and optimize treatment and infection control strategies. From May 1, 2017, to February 28, 2022, they conducted a retrospective analysis of all Shigella isolates identified from stool samples at the clinical laboratories of Harborview Medical Center and the University of Washington Medical Center (Seattle, WA, USA). Species identification, phenotypic susceptibility testing, and whole-genome sequencing were used to characterize isolates. 

Patients’ demographic characteristics and clinical outcomes were examined retrospectively. There were 171 cases of shigellosis included. About 78 (46%) patients were men who have intercourse with other men (MSM), and 88 (52%) were homeless individuals (PEH). Even though 84 (51%) of the isolates were multidrug resistant, 100 (70%) of the 143 patients with data on antimicrobial therapy received the correct empirical treatment. Sequential epidemics of multiple distinct lineages of Shigella flexneri and Shigella sonnei were identified by phylogenetic analysis. Discrete clonal lineages (ten in S flexneri and nine in S sonnei) and resistance traits were responsible for infection in various at-risk populations (e.g., MSM, PEH), allowing for the formulation of practical guidelines for empirical treatment. 

The most prevalent lineage in Seattle was likely introduced to Washington State through international travel, with subsequent domestic transmission among at-risk populations. The parallel emergence of multidrug-resistant strains involving international transmission networks and domestic transmission between at-risk populations caused an outbreak in Seattle. Not only did genomic analysis reveal the outbreak’s origin, but it also directed the most effective testing, treatment, and public health response. Even with multidrug-resistant infections, rapid diagnostics coupled with a thorough understanding of the local epidemiology can enable high rates of appropriate empirical therapy.

Source: sciencedirect.com/science/article/abs/pii/S1473309922008799