OK Wastewater Surveillance
Wastewater surveillance is one tool used by public health to track disease trends in communities. It can also serve as an early warning for disease outbreaks. Some viral infections allow for genetic material from the virus to be found in an infected person’s stool before, during, and after infection. Untreated water samples are taken from water at utility sewersheds and processed in a laboratory setting. Test results tell us how much virus is present by calculating viral particles per liter of water.
Wastewater surveillance can improve our understanding of the actual number of people affected by pathogens like COVID- 19, because it identifies infections from all individuals, including those without symptoms or who do not get tested. Therefore, it can give a more realistic idea of community infection trends since wastewater surveillance isn’t impacted by whether individuals are seeking health care. This information can then be used to inform and educate the public on ways to reduce the spread in their community.
Oklahoma wastewater surveillance is overseen by the Oklahoma State Department of Health (OSDH) in partnership with the University of Oklahoma, OU Health Sciences Center, Tulsa Health Department and Oklahoma City-County Health Department. The project is comprised of 18 utility sites within 15 cities, serving 1,443,944 Oklahomans. The selected cities are geographically distributed across the state and allow for 72% of our state’s population on centralized wastewater to be captured in our surveillance system.
Samples are usually taken from the influent, filtered water at the utility site. There are two types of samples that can give different insights into results. A 24-hour autosampler can be set up to take small amounts of water over the period of time. This type of composite sample gives insight into the community wide level of disease. The 24-hour sample type is best for understanding seasonal trends of disease burden in the community. On the other hand, a grab sample can be taken at a single point in time from the sewershed. This grab sample can tell what is being transmitted through the community during that shorter time frame. Each sample type has its benefits depending on the surveillance needs. Samples taken are stored on ice and transported to the University of Oklahoma microbiology lab for testing.
SARS-CoV-2 (COVID-19) copies per liter is one way of showing how much virus is found in wastewater, expressed as a concentration. This amount tells us how many virus particles are found in every one liter of wastewater. This metric is preferred by the Centers for Disease Control and Prevention’s National Wastewater Surveillance System (NWSS).
Higher wastewater levels can potentially indicate more infected individuals within your community. The data from wastewater surveillance along with the number of cases for a specific illness being reported by health care providers help us understand the presence of disease in a community. Reporting wastewater and other disease specific surveillance data can provide individuals with the tools needed to determine if personal protective measures are necessary to prevent infection in their household.
Samples are collected by wastewater utilities once a week and data are uploaded to the dashboard accordingly.
The OSDH uses wastewater data and other surveillance data (individual case data, hospitalization data, and laboratory positivity data) to evaluate trends and guide public health response. Interpreting these trends allows us to assess the risk of disease in communities and provide public health recommendations to communities. The Viral View dashboard is where this information is displayed.
Wastewater may contain pieces of a virus, but whole virus, the kind that would make you sick, has not been detected in untreated or treated sewage.
By measuring viral concentration at wastewater treatment plants, we only get information about the community that uses that wastewater system. We don’t know if people depositing waste in the sewersheds are residents of that area (versus people who are working or traveling to another area). Many other environmental factors may affect viral levels in wastewater, including water temperature, which is why wastewater data is carefully analyzed for trends and used with clinical surveillance data.
Only data from participating utilities are shown on the dashboard. Utilities voluntarily participate in this surveillance project and are selected to provide a geographically representative snapshot our population.
When a city that is normally listed on the graph is showing “no data” this means a sample has failed recovery for the week. The factors that cause a sample to fail recovery are unable to be controlled. The possibility of failed samples is one drawback to wastewater surveillance and highlights the importance of using it in combination with other forms of surveillance data to monitor infectious disease trends.
When a sample fails recovery, the genetic material in the sample is unable to be removed from the wastewater sample. Factors that impact a sample’s recovery include:
- Weather (lack of rain, heavy rainfall, very cold temperatures, etc.),
- Excess sludge entering the system, or
- Industrial run-off (or any high concentration of chemicals).
When a sample fails to recover genetic material, it is rerun to determine if recovery can be done on the second attempt. If this is successful, the data is reported the following week. If this is unsuccessful, a data point for that week and sample site will be unavailable; however, a sample from that site will be taken the following week as usual. This is why wastewater data should be paired with other sources of data to get a whole picture of infectious disease trends in the state.
