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.