Epidemiology of Single-Etiology Non-Shiga Toxin-Producing Escherichia coli Outbreaks Reported to the National Outbreak Reporting System, with Comparison to Shiga-Toxin Producing E. coli and Shigella, United States, 2009-2023.

Reducing the occurrence of enteric illnesses and outbreaks requires a comprehensive understanding of their epidemiology. While the epidemiology of many diseases, such as Shiga toxin-producing Escherichia coli (STEC) infection, is well-characterized in the United States, the epidemiology of infections caused by E. coli other than STEC (non-STEC) is not. This report describes non-STEC outbreaks reported to the National Outbreak Reporting System (NORS) during 2009-2023. Historically, non-STEC infection was considered travel-associated with limited domestic transmission. During 2009-2023, 230 domestic non-STEC outbreaks were documented, demonstrating that non-STEC can be domestically acquired. Diarrhea (98% of outbreaks), vomiting (79%), and fever (66%) were frequently reported symptoms. Most non-STEC outbreaks were linked to foodborne (38%) or person-to-person (39%) transmission. The majority of reported outbreaks occurred during the latter half of the surveillance period (88%), coinciding with the advent and increased use of culture-independent diagnostic tests (CIDTs). This increase was most pronounced for enteropathogenic E. coli (EPEC). During 2009-2015, six EPEC outbreaks occurred compared with 105 during 2016-2023. This trend underscores the substantial effect of CIDTs on our understanding of enteric disease epidemiology, the importance of continued non-STEC outbreak surveillance and the need for case-based surveillance to inform efforts to prevent these domestically acquired infections.