100 Years of Drinking Water Outbreak Surveillance: Trends and Influence, United States, 1920-2020.

Abstract

To examine trends in US drinking water outbreaks from 1920 to 2020, we evaluated US drinking water outbreaks documented in the National Outbreak Reporting System and from 4 historic publications dating back to 1920. Before the drinking water regulations of the 1970s, enteric pathogens were the most reported (n = 393; 52%) etiologies. Most outbreaks occurred in individual or private water systems (n = 245; 32%). After major regulations, biofilm-associated outbreaks emerged (n = 343; 32%), and most outbreaks (n = 600; 55%) occurred in community water systems. Biofilm-associated pathogens are an emerging concern in water systems. These findings highlight the importance of drinking water regulations, routine inspections of private wells, and building water management programs. Waterborne disease outbreak investigations and reporting to surveillance systems are essential to identifying factors contributing to outbreaks that can be addressed to improve drinking water policy, practices, and public understanding. As pathogens, drinking water distribution systems, and environmental factors change, identifying etiologic agents and contributing factors in waterborne outbreaks can guide future drinking water policies. (<i>Am J Public Health</i>. 2026;116(9): 1387-1396. https://doi.org/10.2105/AJPH.2026.308475).