Anatomy of a Shigellosis Outbreak: Treatment Policies and Implications for Antibiotic Resistance – Central Indiana, 2014

BACKGROUND:   In 2014, cases of shigellosis spread among daycare and school attendees in central Indiana, leading to a large-scale outbreak. The current Indiana Communicable Disease Reporting Rule (410 IAC 1-2.3) excludes laboratory-confirmed shigellosis patients from attending daycare or school until they meet antibiotic treatment requirements or have two successive negative stool cultures. However, due to the self-limiting nature and emergence of antibiotic resistance among Shigella spp., antibiotic therapy is only recommended for severe shigellosis cases. The exclusion policy encourages the use of antibiotic therapy for mild cases and is therefore inconsistent with current treatment recommendations.

METHODS:  

Demographic and clinical data were obtained from 854 outbreak-associated culture-confirmed S. sonnei cases with self-reported onset dates between MMWR weeks 10 and 46. Nine counties with increased incidence of shigellosis cases gathered epidemiological data from cases using standardize investigation forms. Demographic, clinical, and treatment data were then compared between severe cases (those with reported symptoms of bloody stool and/or fever) and mild cases.

RESULTS:  

Over half of the cases (537, 63%) were considered severe. The majority of cases (581, 68%) in the outbreak were aged 1 to 9 years and median age affected was similar for severe cases (6 years) when compared to mild cases (5 years). Most of the cases (749, 88%) were treated with antibiotics: 269 of 317 (85%) mild cases and 480 of 537 (89%) severe cases were treated with antibiotics. The median duration of antibiotic therapy was 4 days for both mild and severe cases. Over half of all cases (499, 58%) were prescribed azithromycin. Amoxicillin, which is not recommended for treating shigellosis, was prescribed for 69 cases (8%). Early susceptibility patterns showed resistance to sulfa drugs; later resistance patterns indicate a combined resistance to sulfa drugs and azithromycin.

CONCLUSIONS:   Both mild and severe cases in this outbreak were treated with antibiotics in order to comply with current Indiana daycare and school exclusion policies. Policies which encourage antibiotic treatment for mild cases may increase emergence of antibiotic resistance. As a result, the Indiana exclusion policy for shigellosis is being revised to match national treatment recommendations and minimize selection pressure for antibiotic resistance.