<i>Shigella sonnei</i> Outbreak Investigation During a Municipal Water Crisis-Genesee and Saginaw Counties, Michigan, 2016.

Abstract

<i>Objectives.</i> To investigate a shigellosis outbreak in Genesee County, Michigan (including the City of Flint), and Saginaw County, Michigan, in 2016 and address community concerns about the role of the Flint water system.<i>Methods.</i> We met frequently with community members to understand concerns and develop the investigation. We surveyed households affected by the outbreak, analyzed <i>Shigella</i> isolate data, examined the geospatial distribution of cases, and reviewed available water quality data.<i>Results.</i> We surveyed 83 households containing 158 cases; median age was 10 years. Index case-patients from 55 of 83 households (66%) reported contact with a person outside their household who wore diapers or who had diarrhea in the week before becoming ill; results were similar regardless of household drinking water source. Genomic diversity was not consistent with a point source. In Flint, no space-time clustering was identified, and average free chlorine residual values remained above recommended levels throughout the outbreak period.<i>Conclusions.</i> The outbreak was most likely caused by person-to-person contact and not by the Flint water system. Consistent community engagement was essential to the design and implementation of the investigation.