Top 5 Takeaways

  1. Significant Legionella Impact: Legionella was the predominant cause of reported drinking water outbreaks, accounting for 86% of biofilm-associated outbreaks, highlighting a growing concern over its presence in public water systems.
  2. High Incidence in Public Systems: Public (community and noncommunity) water systems were implicated in 80% of the outbreaks, emphasizing the need for stringent water quality monitoring and management in these settings.
  3. Enteric Illnesses from Private Systems: Enteric illness outbreaks, primarily linked to private water systems, were implicated in 44% of the cases, underscoring the importance of safe water practices in individual or private settings.
  4. Contributing Factors Identified: The analysis revealed 454 contributing factors across outbreaks, with biofilm formation, inadequate disinfection, and source water contamination being prominent, pointing towards multifaceted strategies for prevention.
  5. Outbreaks and Health Impact: The surveillance period recorded 214 outbreaks associated with drinking water, leading to at least 2,140 cases of illness, 563 hospitalizations, and 88 deaths, indicating the significant health impact of waterborne diseases.

Original Article Author and Citation

Corresponding Author

Jasen M. Kunz, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC. Email:

Suggested Citation

Kunz JM, Lawinger H, Miko S, et al. Surveillance of Waterborne Disease Outbreaks Associated with Drinking Water — United States, 2015–2020. MMWR Surveill Summ 2024;73(No. SS-1):1–23. DOI:


The report outlines the surveillance of waterborne disease outbreaks associated with drinking water in the U.S. from 2015 to 2020. It highlights the increasing prevalence of Legionella in public water systems and underscores the importance of addressing biofilm and enteric pathogens to prevent future outbreaks. Public health departments, regulators, and water system managers can utilize these findings to strengthen water quality monitoring, enhance regulatory standards, and implement comprehensive water management strategies.


Data was collected through the National Outbreak Reporting System (NORS), encompassing epidemiologic, laboratory, and environmental data related to drinking water outbreaks, including those in public and private water systems. The report categorizes outbreaks by etiology, implicated water system, and contributing factors to identify patterns and guide prevention efforts.


The increase in Legionella-associated outbreaks highlights a need for improved detection, reporting, and water management practices. The identification of contributing factors points to potential areas for intervention, such as enhancing disinfection processes and addressing biofilm formation within water systems.


Effective collaboration between public health departments, water system operators, and regulatory agencies is crucial to preventing waterborne disease outbreaks. Ongoing surveillance, coupled with targeted interventions based on the contributing factors identified, will be key to safeguarding public health against future outbreaks.


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