1307. Emergence of Infections Caused by Shigella with Decreased Susceptibility to Azithromycin (DSA) Among Men who Have Sex with Men (MSM) in the United States
Session: Poster Abstract Session: Below the Diaphragm
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
  • 13_243618-A_PTR_Bowen,A_ID Week_final.pdf (180.0 kB)
  • Background:

    In the United States, >400,000 cases of shigellosis are estimated to occur annually. Azithromycin is often used to treat shigellosis among U.S. children and among patients of all ages worldwide. However, clinical laboratories rarely test Shigella for azithromycin susceptibility because testing guidelines have not been published.  We describe the emergence of Shigella with DSA in the United States.


    Health departments submit every 20th Shigella isolate and representative isolates from outbreaks to the National Antimicrobial Resistance Monitoring System (NARMS) at CDC.  Since 2011, NARMS has assessed azithromycin minimum inhibitory concentrations (MICs) for all such isolates.  We defined DSA as MIC >16 µg/mL. We defined a confirmed case as infection caused by Shigella with DSA and a suspect case as infection in which the isolate had unknown azithromycin susceptibility but had a pulsed-field gel electrophoresis (PFGE) pattern indistinguishable from that of an isolate with DSA.  We analyzed routinely collected epidemiologic and clinical details, when available. 


    From Jan 2011 through Mar 2013, we identified 20 confirmed cases with 9 PFGE patterns.  All isolates harbored a plasmid-encoded macrolide resistance gene (mphA) and were resistant to >3 classes of antimicrobials; 12 (60%) were resistant to >4 classes, including one (5%) resistant to ciprofloxacin. Additionally, we identified 49 suspect cases from 2001 – 2013, for a total of 69 cases (50 S. flexneri, 18 S. sonnei, 1 S. boydii) from 19 states. Three (4%) isolates were from blood.  Patients’ median age was 42 years; among the 61 adults, 92% were male. Of those with information available, 10 of 15 were hospitalized, 10 of 11 were MSM, and 8 of 9 were HIV-infected.


    Infections caused by Shigella with DSA appear to be emerging among MSM; illness can be severe.  Shigella’s low infectious dose and the potential for rapid mobility of plasmids increase concern about spread.  Development of azithromycin susceptibility testing guidelines for clinical laboratories would be useful for clinical management and to track this emerging phenotype. We encourage clinicians to culture stool from patients, especially MSM, with symptoms of shigellosis and watch for azithromycin treatment failure.

    Anna Bowen, MD, MPH1, Maria S. Karlsson, PhD1, Katherine Heiman, MPH1, John T. Brooks, MD2, Rebecca Howie3, Regan Rickert3, Barbara E. Mahon, MD, MPH1 and Jean Whichard, DVM1, (1)Centers for Disease Control and Prevention, Atlanta, GA, (2)Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, GA, (3)CDC, Atlanta, GA


    A. Bowen, None

    M. S. Karlsson, None

    K. Heiman, None

    J. T. Brooks, None

    R. Howie, None

    R. Rickert, None

    B. E. Mahon, None

    J. Whichard, None

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