Use this guidance to implement wastewater-based disease surveillance. Wastewater-based disease surveillance is a rapidly developing science, and CDC will continue to update guidance and information as it becomes available.
A minimum set of data is required to interpret SARS-CoV-2 wastewater measurements for use in the COVID-19 response. These data are collected during multiple steps of the sample collection and testing processes.
- Wastewater treatment plant: Information on the wastewater treatment plant service area, number of people served by the utility, and treatment processes is needed to understand the wastewater source.
- Sampling: The sample collection time, date, and location, as well as the sample type (grab or composite) and wastewater flow rate during sample collection are needed to understand sample collection conditions.
- Testing: Information about sample concentration, extraction, and quantification methods, as well as viral recovery efficiency and molecular inhibition measurements are needed to compare wastewater collected from multiple locations and analyzed by different testing laboratories.
To participate in the National Wastewater Surveillance System (NWSS), wastewater treatment plants and testing laboratories should coordinate with their state health department to assess their site’s suitability for wastewater surveillance. NWSS partners must be able to collect the data needed for public health interpretation. Data are submitted to NWSS by state, tribal, local, or territorial (STLT) health departments using a standard collection instrument within the DCIPHER platform. CDC will analyze data reported to NWSS and return results to stakeholders through products such as state reports and dashboards for public health action.
CDC sewage surveillance data lifecycle
This flow chart shows how the NWSS system works. Wastewater from communities is collected by wastewater systems and transported to wastewater treatment plants. Participating utilities collect samples of untreated wastewater or primary sludge. These samples are sent to environmental laboratories for SARS-CoV-2 testing. The testing data, along with the associated utility metadata, is submitted to participating STLT health departments. Health departments submit these data to CDC through the NWSS DCIPHER portal. CDC analyzes the data in real time and reports results to the health department for use in their COVID-19 response.
To interpret SARS-CoV-2 wastewater measurements, polymerase chain reaction (PCR)-based measurements must be converted to sample concentrations and adjusted for testing and wastewater factors, which may change from sample to sample within a wastewater system, and between wastewater systems. Converting PCR measurements to wastewater concentrations must be done prior to submitting data to NWSS. Viral recovery and fecal normalization will be evaluated by the NWSS analytic engine as described below.
SARS-CoV-2 RNA is quantified using PCR technology, either reverse transcription quantitative PCR (RT-qPCR) or reverse transcription droplet digital PCR (RT-ddPCR). Laboratory staff should convert concentration estimates produced by PCR software (in units of copies per reaction or copies per reaction volume) to virus concentrations per volume of unconcentrated wastewater or sludge sample. This conversion accounts for the volume of template used in the PCR (and reverse transcriptase reaction if separate), the concentration factor of nucleic acid extraction, and sample concentration processes.
Presence of viral RNA in a wastewater sample is defined for RT-qPCR measurements as a signal that crosses the threshold at a cycle number