Growing Concern Over Drug-Resistant Shigella in US

Megan Brooks

June 06, 2015

The Centers for Disease Control and Prevention (CDC) continues to receive reports of infections with Shigella strains that are not susceptible to ciprofloxacin and/or azithromycin, the antimicrobial agents most commonly used to treat shigellosis, the agency warned June 4 in a Health Alert Network advisory.

"Most cases have been reported among gay, bisexual, and other men who have sex with men (collectively referred to as MSM) in Illinois, Minnesota, and Montana and among international travelers, but cases are also occurring among other populations. Shigellosis is very contagious and can spread quickly through communities and across different segments of the population," the advisory notes.

The CDC recommends "meticulous" handwashing and other hygiene practices to prevent shigellosis and says patients with symptoms of shigellosis such as diarrhea and fever should see their healthcare provider.

"Clinicians should obtain stool cultures from patients suspected of having shigellosis, counsel patients about shigellosis prevention, and, when treatment is required, select drugs based on antimicrobial susceptibility test results," the CDC advises.

Patients with shigellosis who fail treatment or have prolonged diarrhea should have follow-up stool cultures at short intervals (eg, semiweekly) until the patient has a negative culture, the agency says.

"Shedding of multidrug-resistant shigellae in feces may be prolonged, particularly if the patient was treated with an antimicrobial medication to which the isolate was resistant. Confirming clearance of shigellae from stool will allow more accurate counseling about the timelines appropriate for return to higher-risk activities," the advisory notes.

Recent Multidrug-Resistant Outbreaks

The advisory describes three recent outbreaks of multidrug-resistant Shigella sonnei infections that have occurred in the United States:

1. Extremely drug-resistant shigellosis

As of May 7, 2015, five confirmed cases of extremely drug-resistant shigellosis were identified with illness onset between September 7, 2014, and April 4, 2015, in Illinois and Montana residents. The tested isolates were resistant to ampicillin, ciprofloxacin, nalidixic acid, streptomycin, sulfisoxazole, tetracycline, and trimethoprim/mphA and ermB. Three of the five cases occurred in MSM, two of whom are known to have had diarrhea for more than 14 days. In addition, in March 2015, a Colorado resident who self-identified as MSM was infected with S sonnei that was resistant to ciprofloxacin, nalidixic acid, and trimethoprim/sulfamethoxazole, and had azithromycin minimum inhibitory concentrations higher than 16 μg/mL All six of these cases yielded a pulsed-field gel electrophoresis (PFGE) pattern indistinguishable from those associated with an ongoing cluster summarized for outbreak 2, the CDC says.

2. Ciprofloxacin-resistant shigellosis

From May 2014 through April 2015, 179 cases with one of five highly related PFGE patterns were identified in 34 states and Puerto Rico; roughly half of those who provided information reported international travel before becoming ill. Ten of the cases identified by PulseNet, the national molecular subtyping network for foodborne disease, and another 115 cases without PFGE data were part of an outbreak in San Francisco, California. All San Francisco isolates, and 89% of isolates overall, were resistant to ciprofloxacin. Nineteen cases are known to have occurred among MSM, and several MSM subclusters have been reported throughout the United States. A suboutbreak in a childcare center sickened 16 people. The CDC describes this outbreak in the April 3 issue of the Morbidity and Mortality Weekly Report, as reported by Medscape.

3. Shigellosis with decreased susceptibility to azithromycin

MSM in Chicago, Illinois, and metropolitan Minneapolis/St. Paul, Minnesota, were involved in an outbreak from May 13 through December 8, 2014. Twenty-two isolates displayed highly similar PFGE patterns and had decreased susceptibility to azithromycin, and two additional isolates had indistinguishable PFGE patterns but did not undergo antimicrobial susceptibility testing. All 22 patients were adult men; 15 of 17 with information self-identified as MSM, and 12 were known to have HIV infection. An additional case with an indistinguishable PFGE pattern occurred in an MSM in San Francisco in January 2015, but the isolate was not available for azithromycin susceptibility testing. The CDC described this outbreak in the June 5 issue of the Morbidity and Mortality Weekly Report.

The CDC's National Antimicrobial Resistance Monitoring System has developed a protocol to test Shigella for susceptibility to azithromycin, using the disk diffusion method. Health departments and clinical laboratories that wish to use the protocol for epidemiologic purposes may contact Davina Campbell at xew9@cdc.gov for more information.

More information on this alert is available on the CDC website.

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