How Wastewater Testing Guided the 2022–23 Respiratory Season in Four U.S. Jurisdictions

CDC, MMWR, December 1, 2023.

Wastewater surveillance, the systematic testing of sewage for infectious agents, proved a valuable way to follow SARS-CoV-2 during the COVID-19 pandemic. It has grown from 20 to 53 jurisdictions across the United States, and can increasingly test for other respiratory pathogens. This CDC report shows how the four Centers of Excellence of the National Wastewater Surveillance System (NWSS), in California, Colorado, Houston and Wisconsin, used it to guide public health action in the 2022–23 respiratory season.

The centres

CDC funded the four centres during 2021–22. In 2022–23 their sampling covered 94% of the population in Houston, 67% in California, 65% in Colorado and 50% in Wisconsin. Each used the data differently.

Colorado: early warning for EV-D68

Three Denver sewersheds, serving 1.2 million residents, sent samples every two weeks. Looking back, testing showed enterovirus D68 (EV-D68) rising in wastewater about a month before syndromic and clinical laboratory signals picked it up. Colorado then made wastewater testing part of its EV-D68 surveillance, as an early warning for hospitals planning for surges. The state issued three statewide alerts to hospitals and providers so they could plan staffing and resources.

Houston: schools

Houston sampled weekly at 122 sites (39 treatment plants, 14 lift stations and 69 manholes) serving 2.17 million residents. Forty-eight of the manholes served 48 schools with about 34,000 students, 18.6% of the city's school population, tested for SARS-CoV-2, influenza and RSV. The results:

• vaccination clinics placed where they were needed, which gave 1,058 COVID-19 and influenza doses to 992 students by May 2023;
• 27 reports to schools, so staff could act to prevent spread;
• a public dashboard, and alert notifications about surges, with 698 registered users linked to 46 schools.

California: 98 sewersheds

California sampled 98 sewersheds, daily to weekly, in 41 counties covering about 26 million residents (67% of the population), for SARS-CoV-2 variants, RSV and influenza. Local health departments use the results in decisions and in messages to communities, providers and health systems, including advice on vaccines and masking, through dashboards, weekly reports and the media.

Wisconsin: variants first

Wisconsin tested for SARS-CoV-2 at 43 sites covering about 2.93 million residents. By 2023 its public dashboard with alerts had more than 250,000 views and its genomic sequencing dashboard more than 6,000; weekly reports went to local health departments and water utilities. The sequencing sometimes found variants, such as BA.5 and XBB, in wastewater before case reports and hospitalizations did. Twenty sites covering about 2.48 million residents were also tested for influenza A and B and RSV; their levels tracked emergency department visits closely in 2022–23, rising weeks before the visits did, so the monitoring continues into 2023–24.

What the centres showed

Wastewater data matched clinical surveillance while giving local, timely coverage, and sometimes useful lead time. Together with clinical data, it guided decisions on where to put resources and vaccination clinics, when to update clinical guidance, and when to send alerts once trends crossed baseline thresholds. The centres built public and internal dashboards for their partners and communities, and in 2022–23 turned wastewater results into real-time action against several respiratory pathogens at once.

Sources

• Valencia D, Yu AT, Wheeler A, et al. "Notes from the Field: The National Wastewater Surveillance System's Centers of Excellence Contributions to Public Health Action During the Respiratory Virus Season — Four U.S. Jurisdictions, 2022–23." MMWR 2023;72(48). https://www.cdc.gov/mmwr/volumes/72/wr/mm7248a4.htm
• The report gives Houston's dashboard views as about 350,000 in its text and more than 362,000 in its summary box, and Wisconsin's SARS-CoV-2 sampling as daily to weekly in one and weekly or biweekly in the other; neither figure is repeated here.