479. An Outbreak of Shigella sonnei with Decreased Azithromycin Susceptibility, Los Angeles County 2012
Session: Poster Abstract Session: Public Health
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Background: In 2012, the Los Angeles County Department of Public Health (LAC-DPH) investigated an outbreak of shigellosis at a private bridge club. This is the first known outbreak of Shigella sonnei with decreased susceptibility to azithromycin in the United States.


Cases were persons with 1) illness clinically compatible with shigellosis or 2)S. sonnei isolated from stool and epi-linked to the club during May 22–26, 2012. Methods included interview of bridge club workers and members who attended during the week of May 22; inspection of the club premises and food service; and collection of stool specimens for laboratory analysis.


Forty-three cases (4 staff, 39 members) were identified. Cases were 55% female and average age of 75.3 years (range: 54-98 years). Symptoms reported included diarrhea (95%), cramps (71%), and fever (57%). Average duration of illness was 5.9 days (range: 1-14 days).  Persons 80+ years were more often hospitalized (OR=40.5; CI=[4.3-383.3]). Employees denied illness prior to or during week of May 22. The implicated source was food prepared at the club by one employee. Eight employees and 35 members submitted stool to LAC-PH for testing. S. sonnei was isolated from 12 stool samples; 1 co-owner, 2 teachers, 1 food handler and 8 members. PFGE (Pulsed-Field Gel Electrophoresis) results on 10 isolates all had an indistinguishable pattern. Four isolates submitted to CDC's National Antimicrobial Resistance Monitoring System (NARMS) displayed resistance to streptomycin, sulfisoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Unlike most Shigella isolates tested by NARMS, these isolates showed elevated azithromycin minimum inhibitory concentrations (MICs) of >16 µg/mL and harbored a plasmid-encoded macrolide resistance gene, mphA.

Conclusion: Although sporadic illness from Shigella strains with increased azithromycin MICs has occurred, this first documented U.S. outbreak may indicate increased circulation of such strains. Clinical management of such illnesses may be complicated in children. Guidelines for azithromycin susceptibility testing and criteria for interpretation of MICs for Shigella species have not been published. We ask clinicians to report azithromycin treatment failure of shigellosis patients to public health and to submit such isolates for analysis.

Roshan Reporter, MD, MPH, Acute Communicable Disease Control Program, Los Angeles County Dept. of Public Health, Los Angeles, CA and Marifi Pulido, MPH, PhD, Acute Communicable Disease Control Program, Los Angeles County Department of Public Health, Los Angeles, CA


R. Reporter, None

M. Pulido, None

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