The Georgia Department of Public Health (DPH) is participating in the Centers for Disease Control (CDC) National Wastewater Surveillance System (NWSS). In April 2022, the Georgia NWSS (GA NWSS) program began conducting wastewater sampling to better understand COVID-19 trends in Georgia. When used alongside other public health surveillance methods, wastewater surveillance can provide insight into community-level transmission.

Wastewater treatment facilities (WWTF) collect water samples twice per week. These raw wastewater samples are sent to the Georgia Public Health Laboratory (GPHL), where they are tested for a variety of pathogens. This report includes the respiratory viruses that GA NWSS currently tests for: SARS-CoV-2 (COVID-19), RSV, Flu A, and Flu B. GA NWSS also tests for Mpox at select sites; these data can be found on the CDC’s U.S. Monkeypox Wastewater Data page.

The Georgia NWSS Program is a collaboration between wastewater treatment facilities (WWTFs), state and district public health departments, universities, and national partners including CDC NWSS and WastewaterSCAN (WWScan).

There are many reasons why a pathogen’s concentration in wastewater may change, including the number of people in a community, how many people in the community are sick, whether there is stormwater runoff, and even how a lab tests the samples.

Because of this, wastewater data cannot be interpreted the same way as traditional surveillance. Comparing normalized concentration values from one county to another may be misleading due to differences in the county that are unrelated to the actual amount of disease present in the community. One example of this is if one county has a larger percentage of the population that uses septic tanks. Directly comparing concentrations of one pathogen to another is also challenging, because some pathogens are easier to detect in wastewater than others or that different people may shed more or less virus into wastewater even if infected with the same pathogen.

With this in mind, the best way to look at wastewater data is by looking at the same location and pathogen over time. By looking at the same location and pathogen, we might be able to find a pattern or direction of the data, which is called a ‘trend’. When combined with other surveillance methods, wastewater surveillance data can provide a holistic picture of disease in a community.

Wastewater treatment facility (WWTF) partners generally collect two raw wastewater samples per week for the GA NWSS program. This raw wastewater includes feces and urine, as well as anything that enters the public sewer from your home, school, or business, typically from sinks and toilets. Some sewer systems may also include stormwater runoff.

Once the samples arrive at the Georgia Public Health Laboratory (GPHL), genetic material is extracted from each wastewater sample. GPHL scientists then test the wastewater sample for the presence of SARS-CoV-2, Flu A, Flu B, or RSV virus and measure the concentration of each virus. This information provides public health with information on community transmission and the change in trends over time.

The limit of detection (LoD) is a cut-off concentration unique to each pathogen. The LoD is the smallest amount of genetic material that can be reliably detected through molecular testing. A result is considered a ‘non-detect’ when the amount of viral genetic material in the sample is below the LoD. This does not necessarily mean that the pathogen isn’t in the community – it could still be present at very low levels - but the test can’t confidently tell it apart from background noise or other signals. To account for this, measurements below the LoD are shown on graphs as estimated concentrations, rather than exact values.

To aid in interpretation of Flu and RSV data these graphs include a dotted black line which represents the average LoD for that county. In some cases, a sample may appear above the average LoD line but still be classified as “below the LoD” or “non-detect”. This happens because the LoD is normalized based on the population served by the WWTF and the daily flow rate, as described below, resulting in a slightly different normalized LoD from day to day.

Normalization is a statistical method that reduces variability across different facilities. GPHL reports the raw concentration of viral genetic material, but that concentration can be affected by factors such as flow rate, number of gallons of wastewater a facility treats per day, and the number of persons served by the facility. GA NWSS normalizes by flow rate and population size (estimated number of persons served by the facility), and reports concentration as viral gene copies per person

As of 05/07/2026, the GA NWSS External reports adjusted the normalization process to utilize U.S. liquid gallons for unit conversion to align with CDC NWSS standards. This change may cause small differences in the normalized concentration values, but it does not impact the overall trends or how the results should be interpreted. Raw concentration values remain the same.

Smoothing techniques are used to fit a trendline to the data and produce final concentration estimates. These estimates may change as new data is entered. These values are reported as ‘estimated concentration’ and can be seen by hovering over the trendline on the graphs. Concentrations of viral targets in wastewater can be very variable day to day and show sharp spikes or decreases that may not be reflective of overall trends. The estimated concentration provides a more interpretable trend for the pathogen.

Georgia Department of Public Health publishes a weekly pan-respiratory report (link) which includes statewide summary values of wastewater surveillance data. Statewide summary values are calculated by first generating a weekly normalized concentration for each target at each sewershed via geometric mean. These values are averaged to calculate an overall weekly statewide normalized value. Finally, an estimated weekly statewide normalized value is calculating using smoothed techniques as described above.

There are currently 13 counties with WWTFs that are active in the GA NWSS program. Therefore, the statewide wastewater summary cannot provide a comprehensive representation of wastewater levels across all of Georgia. Rather, this summary uses the counties where GA NWSS has active facilities to indicate the overall trend of that pathogen in wastewater in Georgia.

Wastewater target levels are displayed as “very low,” “low,” “medium,” and “high.” Very low refers to concentrations below the average limit of detection from the previous season. Cutoffs for low, medium, and high are calculated from the first, second, and third tertiles of the concentrations above the limit of detection from the previous season. Cutoffs are based on one year of data and are recalculated each season; on April 1 and October 1 for COVID-19 and on August 1 for influenza and RSV. A county’s level will be shown as “Not enough data” if there is no recent sample.

Statewide wastewater target levels are calculated similarly, using the smoothed weekly statewide normalized values as described above. For newer facilities that do not have data for the entire previous season, statewide cutoffs are used in combination with recent data to calculate cutoff concentrations.