January 16, 2019
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Shigella shows high resistance to azithromycin, ciprofloxacin

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More than half of tested Shigella isolates obtained from men who have sex with men, or MSM, in an Australian state demonstrated resistance to azithromycin, and almost one-fifth were resistant to ciprofloxacin, according to findings published in Clinical Infectious Diseases.

Each year, shigellosis causes an estimated 190 million cases of diarrhea worldwide, according to Danielle J. Ingle, PhD, postdoctoral fellow at the Australian National University and University of Melbourne, and colleagues.

“In low- and middle-income countries, the burden of shigellosis is concentrated in children, with inadequate sanitation and contaminated food and/or water the most common mode of acquisition. In contrast, shigellosis in high-income countries occurs predominantly in returning travelers, or in MSM,” they wrote. “In many high-income countries there are increasing reports of locally-acquired shigellosis in MSM, with endemic shigellosis in males in these countries often considered a sexually-transmitted infection.”

Shigella has shown increasing resistance to first- and second-line treatments, such as ciprofloxacin, azithromycin or trimethoprim-sulfamethoxazole, and antimicrobial-resistant Shigella has been declared a “major public health threat” by the CDC and WHO, the researchers noted.

Ingle and colleagues conducted a population-level study of all cultured Shigella isolates in Victoria, Australia, between Jan. 1, 2016, and March 31, 2018. The isolates were sent to the Microbiological Diagnostic Unit Public Health Laboratory for antimicrobial susceptibility testing, whole-genome sequencing (WGS) and bioinformatic analysis. The researchers used enhanced surveillance forms and interviews to collect risk factor data about travel and sexual exposure.

According to Ingle and colleagues, 50.6% of the 541 isolates that were tested for susceptibility harbored resistance to azithromycin and 17.6% were resistant to ciprofloxacin. They identified an S. sonnei lineage and S. flexneri 2a lineage associated with MSM. Findings showed that 92.4% of isolates in the MSM-associated S. sonnei lineage contained mutations associated with reduced susceptibility to azithromycin, trimethoprim-sulfamethoxazole and ciprofloxacin.

Analysis suggested that multidrug-resistant plasmids across Shigella species and lineages are spread globally but are predominantly associated with MSM, Ingle and colleagues said. They underscored that the ongoing public health threat caused by resistant Shigella affects not just Australia, but the world.

“We demonstrate that local and global dissemination of clinically significant antimicrobial-resistant Shigella spp. is driven largely by the spread of highly related, multiresistant plasmids that are not restricted by Shigella species or lineage,” Ingle and colleagues wrote. “Urgent multidisciplinary public health measures are required, including enhanced contact tracing of multiresistant cases of shigellosis (which could be informed by WGS data), improved antimicrobial stewardship, improved information on clinical outcomes of resistant shigellosis, and heightened awareness of shigellosis as an STI.” – by Marley Ghizzone

Disclosures: Ingle reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.