About the wastewater program

What is wastewater surveillance?

Wastewater surveillance is a public health tool that involves collecting and analyzing sewage to understand disease trends in our communities, without testing individuals. People shed viral, bacterial, and fungal particles in wastewater through everyday activities, such as using the toilet, showering, or washing their hands, sometimes even before showing symptoms. Wastewater utilities collect samples twice weekly and submit them to labs to test using sensitive methods like polymerase chain reaction (PCR). This helps detect which pathogens (germs) are circulating. Since the data represents a whole community, we can determine trends of illness for a community without relying on people seeking medical care and testing. This is cost-effective and especially useful when testing individual patients isn’t possible or hard to do. Wastewater surveillance data helps public health officials understand how diseases are spreading, know where to focus testing and vaccination efforts, and make timely, evidence-based decisions for community health.

Sentinel Surveillance System (SSS)

To build a sustainable wastewater surveillance model in Colorado, we launched a Sentinel Surveillance Site system on Aug. 1, 2024. This approach allows us to prioritize emerging pathogens and monitor select targets at 21 wastewater utilities across the state. These sites include one utility in each of Colorado’s 10 emergency response regions (some with multiple plants) that serve the largest population in that region, three large Denver metro utilities, and four utilities in high-tourism areas that voluntarily participate in our program. After a re-evaluation of the system based on public feedback and data from expanded pathogen surveillance, we added an additional site in the northern region of the state in October 2025.

Although we reduced the number of participating utilities by two-thirds, the sentinel model still covers 50% of Colorado’s population and provides data comparable to our previous statewide approach. We also established an emergency surveillance system with previously participating utilities, which is activated during public health responses for expanded coverage.

Benefits and limitations of wastewater surveillance

A major advantage of wastewater surveillance is its ability to monitor the health of entire communities in a cost-effective and non-invasive way. By analyzing what’s present in wastewater, we can track disease trends across a population without relying on individuals to seek testing or report symptoms. This overcomes some of the challenges of traditional case reporting, including the delay between infection and testing. This broad, community-level approach makes it possible to detect shifts in disease levels even when clinical testing is limited or inconsistent. 

However, like any surveillance system, wastewater surveillance has limitations. It cannot tell us exactly how many people are infected, nor can it pinpoint when someone became sick or has recovered. Because pathogens can be shed before, during, and after the onset of symptoms, there is a delay that makes it hard to pinpoint exactly when or where an infection started. Wastewater surveillance detections may also come from animal or environmental sources and might not necessarily indicate human infection. Importantly, while wastewater surveillance data is valuable for guiding public health discussions, the Program itself does not set public health actions or rules. Decisions about messaging, interventions, or response strategies are made by public health leaders in consultation with many data sources, including but not limited to wastewater surveillance trends.

In Colorado, wastewater surveillance adds an important layer of insight to our disease monitoring system. It enhances preparedness efforts and helps inform decisions, but it works best when interpreted alongside other public health surveillance data.

How testing works

Wastewater utilities in our sentinel model voluntarily participate to collect and  submit wastewater samples to our lab twice weekly. Upon receipt, our lab determines whether the specific pathogen is present or absent in the sample and how much is present. Samples that test positive for COVID-19 are forwarded to our sequencing team to identify the variants present. Similarly, positive Influenza A samples are sequenced to determine the specific subtype detected in the wastewater.

While sampling typically occurs twice weekly year-round, holiday weeks may result in canceled or delayed sample collection due to limited staffing and holiday leave. As a result, you may notice fewer or delayed data updates on our dashboard during these times.
 

Stay updated

If you are interested in staying updated about activities and improvements in our program, we invite you to join our e-mail list! Updates include news about our dashboard, data, lab methods, and other programmatic developments. To join, please fill out the Wastewater Surveillance Public Interest Form. We also encourage you to explore our Colorado NWSS Center of Excellence website, which features an Educational Resources page where we regularly post training videos, webinars, recent publications, and more. For national context and additional information, check out the CDC’s National Wastewater Surveillance System (NWSS) website. 

Additional questions? 

Visit our FAQ page for more details.