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Healthcare professionals should be on the lookout for an increase in extensively drug-resistant (XDR) Shigella infections (shigellosis) and should report cases to local or state health departments, the CDC said in a .

Given that Shigella bacteria are easily transmissible (through as few as 10-100 organisms) and antimicrobial treatment options are limited, the agency also asked healthcare providers to educate patients and communities at increased risk about prevention and transmission.

Historically, the infection has been most common in children ages 1 to 4 years in the U.S., but the CDC has reported a rise in antimicrobial-resistant Shigella infections among men who have sex with men, people experiencing homelessness, international travelers, and people with HIV in .

The agency detected a recent rise in XDR Shigella infections through national surveillance systems, with 5% of infections caused by XDR strains in 2022, up from 0% in 2015. From 2015 to Jan. 22, 2023, CDC has received reports of 239 XDR Shigella isolates.

Among the recent infections, median age of patients was 42 years. Of the 232 patients with available information, 82% were men, 13% were women, and 5% were children. Of the 41 patients who provided information about recent sexual activity, 88% reported male-to-male sexual contact.

This acute enteric infection can cause "inflammatory diarrhea that can be bloody and may also lead to fever, abdominal cramping, and tenesmus," the agency noted.

XDR strains can also spread antimicrobial resistance genes to other enteric bacteria, adding to the "potentially serious public health concerns," the CDC said.

Healthcare professionals should consider shigellosis in the differential diagnosis of acute diarrhea, especially in patients at higher risk, and should ask patients about relevant exposures and social history, including sexual history and travel.

Shigella bacteria are transmitted by the fecal-oral route, person-to-person contact including sex, and through contaminated food and water. The CDC said patients with shigellosis should stay home; abstain from sex; wash hands often, especially around sexual activity; not prepare food for others; and stay out of recreational water.

"Currently, there are no data from clinical studies of treatment of XDR Shigella to inform recommendations for the optimal antimicrobial treatment of these infections," the agency wrote. "As such, CDC does not have recommendations for optimal antimicrobial treatment of XDR Shigella infections."

XDR Shigella bacteria are resistant to azithromycin, ciprofloxacin, ceftriaxone, trimethoprim-sulfamethoxazole, and ampicillin.

According to the CDC's , which shows predicted antimicrobial resistance based on preliminary data, Shigella isolates tested in 2023 with the most resistance to ciprofloxacin are concentrated in Washington state, and, to a lesser extent, Utah and New Mexico.

While most patients recover from shigellosis without treatment with antimicrobials, the CDC recommended antimicrobial susceptibility testing to guide antimicrobial treatment selection when needed. Though options for XDR shigellosis are lacking in the U.S., a suggested a potential strategy of oral pivmecillinam (not commercially available in the U.S.) and fosfomycin, or IV carbapenems and colistin.

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