Key points:

• Limitations of Traditional Methods: The study highlights significant limitations in traditional culture-based methods for detecting fecal indicator bacteria (FIB), such as E. coli. These methods fail to account for bacteria bound in aggregates, leading to substantial underestimation of waterborne disease risks. This underestimation can severely skew public health risk assessments and highlights the limitations of the current regulatory frameworks to protect water users in waters containing fecal or sediment particles, such as urban rivers subject to combined sewer overflows.
• ALERT Methodology: The research uses ALERT as a new technology for automated rapid method for comprehensive quantification of culturable bacteria. ALERT can measure both planktonic (free-floating) and comprehensive bacteria (which are bound in aggregates, such as on fecal or sediment particles), providing more accurate risk assessments. This method revealed that aggregate-bound bacteria are present in much higher quantities than detected by traditional methods, creating a major and currently non-monitored risk. This risk is particularly highlighted in the water of the Seine river in Paris, venue for the 2024 Olympic Triathlon and Marathon swimming events.
• Implications for Water Safety: The study's findings underscore the need for updating global water safety regulatory frameworks to include methods that can accurately measure comprehensive E.coli counts, including aggreagate-bound bacteria. Incorporating such comprehensive methods can improve water quality monitoring, particularly in recreational and agricultural water uses, but also for drinking water assessment in remote locations without managed distribution networks. ALERT can better protect public health by providing more accurate risk assessments.