First report of sexually transmitted multi-drug resistant Shigella sonnei infections in Switzerland, investigated by whole genome sequencing

Vladimira Hinic,Helena Seth-Smith,Marcel Stöckle,Adrian Egli,Daniel Goldenberger

doi:10.4414/smw.2018.14645

Vladimira Hinic, Helena Seth-Smith + Show 3 more

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https://doi.org/10.4414/smw.2018.14645

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Abstract

Shigella sonnei causes foodborne infections, but has recently also been described as a sexually transmitted infection (STI), with increased levels of antimicrobial resistance. We describe three cases of sexually acquired Shigella sonnei infection - the first report of this emerging infection in Switzerland. We used in-house whole genome sequencing (WGS) to investigate possible transmission routes and epidemiological correlations between the three cases. The genomic analysis demonstrated that two of three case isolates were very closely related, with only two single nucleotide polymorphism differences between them, despite being isolated from two unrelated patients at time-points six months apart, and the infections having been acquired at different geographic locations within Europe. All three isolates were found to fall within two of the clusters (1 and 7) defined within UK men who have sex with men (MSM) isolate populations, but with higher divergence, suggesting a more diverse pool circulating within Europe. Phenotypic testing confirmed the genotypic findings, with all three isolates azithromycin resistant, and two out of three resistant to quinolones. This report underlines the importance of the implementation of new sequencing technologies in the investigation of epidemiological aspects of this STI circulating in the population of MSM. In such cases, therapy should always be guided by antimicrobial susceptibility testing owing to increasing resistances. Greater awareness of this emerging sexually transmitted infection is needed.

Highlights

Shigellosis is a well characterised foodborne infection, classically associated with diarrhoea after travel to endemic countries
We report for the first time in Switzerland, three cases of sexually transmitted Shigella sonnei infection in men who have sex with men (MSM), diagnosed in Basel but acquired from three different geographic locations
Two of the isolates were very closely related, with only two Single nucleotide polymorphism (SNP) differences between them. They are unlikely to have resulted from direct transmission as: the case dates were more than 6 months apart; they were assumed to have been acquired at two different geographic locations (Berlin and Paris/Munich); and the estimated substitution rate of S. sonnei genomes is 2.2 SNPs per chromosome per year [12]

Summary

Introduction

Shigellosis is a well characterised foodborne infection, classically associated with diarrhoea after travel to endemic countries. Infection requires an exceptionally low infectious dose of 10 or fewer bacteria [1]. Since 2001, cases of sexually transmitted Shigella spp. among men who have sex with men (MSM) have been reported with increasing frequency, becoming an important public health problem in many countries [2, 3]. Increasing antimicrobial resistance in Shigella spp. has been reported [2, 6, 7]. We report for the first time in Switzerland, three cases of sexually transmitted Shigella sonnei infection in MSM, diagnosed in Basel but acquired from three different geographic locations. The isolates were characterised by phenotypic antimicrobial susceptibility testing (AST), and whole genome sequencing (WGS)

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