CDC Wastewater Surveillance (NWSS)
- Source
- CDC National Wastewater Surveillance System
- Update Cadence
- Varies by site
- Coverage
- 800+ sampling sites across the U.S.
- Official URL
- View source
What It Measures
NWSS measures the concentration of viral genetic material (RNA) in untreated wastewater at treatment plants across the country. It currently monitors SARS-CoV-2 (COVID-19), influenza A, and RSV.
How It Works
Participating wastewater treatment plants collect samples regularly and send them to labs for testing. The concentration of viral RNA is measured and normalized by population size to allow comparisons across sites.
What It Tells You
Wastewater surveillance captures the entire community — including people who never seek medical care. It often detects increases in viral activity 1-2 weeks before clinical data shows a rise, making it an early warning signal.
Limitations
- Geographic coverage is uneven — some areas have multiple sampling sites while others have none.
- Cannot tell you how many people are sick, only that virus is present in the community.
- Concentration levels are affected by rainfall, industrial discharge, and lab methodology.
- Cannot distinguish between symptomatic and asymptomatic infections.