Standard risk assessment methodologies are significantly underestimating fecal indicator bacteria (FIB) loads in contaminated water, including recreational waters used for the 2024 Olympics, a new study reveals.
The article, by scientists from water monitoring experts Fluidion, proposes a new methodology which was able to demonstrate that the actual FIB levels—including aggregate-bound bacteria—may in fact be substantially higher, with implications for water safety practices worldwide to the point of rendering them useless in certain instances.
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The paper, ‘ Addressing Underestimation of Waterborne Disease Risks Due to Fecal Indicator Bacteria Bound in Aggregates’, appears in the Journal of Applied Microbiology, an Applied Microbiology International publication.
Persistent threat
The research addresses the persistent threat of waterborne pathogens, which continue to pose significant health risks worldwide, although in different ways across developed countries and low- and middle-income countries (LMICs), warned corresponding author and Fluidion CEO Dan E Angelescu.
“In developed regions, while advanced water treatment and disinfection have made drinking water safer, substantial risks remain in agricultural, recreational, and athletic water use. Contaminated irrigation water has caused E. coli outbreaks linked to produce, resulting in costly recalls and public health issues,” he said.
“Recreational waters—popular for swimming, triathlons, and other activities—have also seen illness outbreaks despite passing regulatory testing.
“Our research highlights a previously overlooked reason for these issues: traditional water monitoring methods fail to detect fecal bacteria bound in aggregates, leading to underestimates of contamination levels and health risks. This underestimation is especially relevant in urban and agricultural waters affected by recent sewage contamination: sewer system overflows, illicit discharges, or insufficiently treated wastewater.”
Matter of life and death
In LMICs, the water quality crisis remains a matter of life and death, he said.
“Contaminated water directly impacts vulnerable populations, with preventable waterborne diseases causing over a million deaths annually, disproportionately affecting children and the elderly. Limited current access to reliable water monitoring further exacerbates the problem, especially in remote or disaster-stricken areas where safe water is often unavailable.”
The research set out to evaluate the prevalence of aggregate-bound bacteria across various water environments and to demonstrate how their presence can distort risk assessments, leading to an overly optimistic view of water quality.
By identifying these previously undetected bacterial loads, the team aimed to highlight the urgent need for more comprehensive monitoring methods and portable, field-ready instruments that could be deployed even in remote locations, an approach that is essential for accurately assessing contamination levels and addressing the global water safety gap in both developed and developing regions. The team used the ALERT line of rapid microbiology analyzers that are manufactured by Fluidion.
Current methods
They found that in waters containing fecal particles or aggregates, current standard microbiological risk assessment methods fail to accurately quantify FIB, routinely underestimating their presence—sometimes by orders of magnitude.
This shortfall arises from the intrinsic limitations of approved culture-based methods, which treat an entire aggregate as if it contains only a single bacterium, regardless of the actual number of E. coli present within.
To address this, the researchers developed a novel methodology and instrumentation capable of separately measuring free-floating and aggregate-bound culturable FIB, enabling them to capture the full bacterial load and analyze its distribution across aggregates of different sizes.
Surprising findings
“What we found was surprising: in diverse water sources—including the 2024 Olympic site’s recreational waters, sea beaches, irrigation canals, and wastewater treatment effluent—our measurements frequently revealed bacterial counts far higher than those produced by standard methods, indicating serious flaws in current risk assessment practices,” Dr Angelescu said.
“Our findings were further confirmed through microscopy and molecular measurements (RT-qPCR) for FIB, underscoring the extent of this oversight. Like seeing only the tip of an iceberg, the standard methods capture just a fraction of the true contamination.
“This study is the first to quantify the extent of the “aggregate” issue, enabled by our novel methodology and instrumentation. Our findings reveal that standard methods, which form the basis of epidemiological studies and current regulations, fall short in accurately assessing risk across many water types.
“These traditional methods assume a uniform distribution of culturable bacteria, but our research demonstrates that this assumption is often flawed, with significant implications for global water safety.”
Sheer scale of issue
Most surprising was the sheer scale of the issue and its widespread presence across various geographical regions and water types.
“ We observed a significant excess of fecal indicator bacteria bound within aggregates that completely eludes standard detection methods. This discrepancy wasn’t minor but profound—standard methods underestimated contamination levels by large multiples and, in some cases, by several orders of magnitude,” Dr Angelescu said.
“Our monitoring of major events, including the 2024 Olympic Games, confirmed these findings. A separate publication on this work is currently in preparation.
Lack of awareness
“We were equally struck by the lack of awareness of this issue within the microbiology and regulatory communities. Despite the seemingly clear nature of this effect, it has gone largely unrecognized, pointing to a human tendency to sideline what is challenging to measure rather than address it directly.
“Even in the face of scientific evidence, this oversight persists, highlighting the urgent need for a change of paradigm, and a more rigorous approach to water safety practices worldwide.”
The findings reveal that current water quality monitoring practices severely underestimate bacterial contamination, especially in cases where fecal indicator bacteria are bound within aggregates.
“This has real-world implications: in developed regions, it means that risk assessments for agricultural and recreational waters may be inaccurately low, potentially exposing people to unseen health risks. For example, contaminated irrigation water can introduce pathogens into food supplies, leading to costly and dangerous E. coli outbreaks, while recreational waters may present hidden risks for swimmers and athletes despite passing standard tests,” Dr Angelescu said.
Urgent implications
“In low- and middle-income countries (LMICs), where waterborne diseases are already a leading cause of illness and death, the implications are even more urgent. Without reliable monitoring methods and automated instrumentation that capture the true scope of contamination, vulnerable populations, especially children and the elderly, remain at high risk.
“Prioritization of water sources based on accurate quantitative microbiological risk assessments is essential for preventing preventable diseases and reducing mortality in these communities.
“This research underscores the necessity for new, comprehensive monitoring approaches that reflect actual contamination levels and for deploying these methods widely. It also points to the importance of adopting automated field instrumentation, such as the Fluidion ALERT instruments used in this study, that could allow testing to be performed wherever it is needed, and not limited to the very few areas, globally, serviced by water quality laboratories.
Need to update regulations
“Our research points to the urgent need for updated regulations that reflect the latest scientific insights and provide greater public protection.
“At the same time, it supports the adoption of field-ready instrumentation, now commercially available, to enable direct water safety measurements at remote sites where they are critically needed and where laboratory access is limited or nonexistent. This could have a major impact not only in the developing world (where water quality is often a matter of life and death), but also in the developed countries, where waterborne disease burden could be reduced.”
The work was performed by Fluidion’s teams based in Paris and Los Angeles, spanning multiple countries on two continents. It was supported by the European Union through the H2020 program (Project: Digital Water City), and by the US Department of Agriculture through the SBIR program (Project: Alert-Ag++).
‘Addressing Underestimation of Waterborne Disease Risks Due to Fecal Indicator Bacteria Bound in Aggregates’ appears in the Journal of Applied Microbiology.
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