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CDC Health Alert: Ciprofloxacin- and Azithromycin-Nonsusceptible Shigellosis in U.S.
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. 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 CDC says.
As of May 7, 2015, five confirmed cases of extremely drug-resistant shigellosis were identified with onset dates from September 7, 2014 through April 4, 2015, in Illinois and Montana residents. The isolates were tested by the CDC’s National Antimicrobial Resistance Monitoring System (NARMS) and were found to be resistant to ampicillin, ciprofloxacin, nalidixic acid, streptomycin, sulfisoxazole, tetracycline, and trimethoprim/sulphamethoxazole; to have azithromycin minimum inhibitory concentrations (MICs) of greater than 16 mcg/mL; and to harbor macrolide resistance genes mphA and ermB. Of these five cases, three self-identified as MSM, and two were known to have experienced diarrhea for more than 14 days.
In addition, in March 2015, a Colorado resident who self-identified as MSM was infected with Shigella sonnei that was resistant to ciprofloxacin, nalidixic acid, and trimethoprim/sulphamethoxazole, and that had azithromycin MICs of greater than 16 mcg/mL.
From May 2014 through April 2015, 179 cases with one of five highly related pulsed-field gel electrophoresis (PFGE) patterns were identified in 34 states and Puerto Rico; approximately half of those who provided information reported international travel before the onset of illness. Ten of the cases identified by PulseNet and another 115 cases without PFGE data were part of an outbreak in San Francisco, California. All of the San Francisco isolates, and 89% of isolates overall, were resistant to ciprofloxacin. Nineteen cases are known to have occurred among MSM, and several MSM sub-clusters have been reported throughout the U.S. A sub-outbreak in a child care center made 16 people ill.
MSM in Chicago, Illinois, and metropolitan Minneapolis/St. Paul, Minnesota were involved in an outbreak of shigellosis from May 13 through December 8, 2014. Twenty-two isolates displayed highly similar PFGE patterns and showed decreased susceptibility to azithromycin; two additional isolates had indistinguishable PFGE patterns but did not undergo antimicrobial susceptibility testing. All 22 patients were adult males; 15 of 17 with information self-identified as MSM, and 12 were known to have human immunodeficiency virus (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 encourages clinicians to:
- Obtain stool cultures from patients suspected of having shigellosis.
- Base treatment for shigellosis, when needed, on the antimicrobial susceptibility profile of the individual isolate or, during a local outbreak, that of the outbreak strain.
- Counsel shigellosis patients about the importance of meticulous hand washing after using the toilet, and avoiding activities most likely to transmit the infection to others, such as preparing food for others, swimming, group play among young children, and certain sexual activities (e.g., anal rimming or fisting).
- Recommend that symptomatic contacts of shigellosis patients, particularly those suspected to have a multidrug-resistant strain, seek health care.
- Obtain follow-up stool cultures at short intervals (e.g., semiweekly) for shigellosis patients with treatment failure or prolonged diarrhea until the patient has a negative culture. 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 the clearance of shigellae from stool will allow more accurate counseling about the timelines appropriate for a return to higher-risk activities.
Source: CDC; June 4, 2015.