Wastewater surveillance offers insights into community-wide health trends by analyzing sewage for genetic material from viruses like SARS-CoV-2, the virus responsible for COVID-19. San Diego has been at the forefront of this approach, utilizing wastewater data to understand and respond to the pandemic within its communities. This surveillance provides a broad overview of viral activity, complementing individual clinical testing efforts.
The Science Behind Wastewater Monitoring
The SARS-CoV-2 virus, which causes COVID-19, is shed by infected individuals in their bodily waste, particularly in stool. This shedding occurs regardless of whether a person experiences symptoms. The viral genetic material, specifically RNA, then enters the wastewater system as part of human sewage.
To detect the virus, wastewater samples are collected from sewer lines or treatment plants. These samples contain a mixture of waste from many individuals, providing a collective snapshot of a community’s health. In the laboratory, specialized techniques such as reverse transcription quantitative polymerase chain reaction (RT-qPCR) are used to detect and quantify the SARS-CoV-2 RNA. This molecular method amplifies specific genomic regions of the virus, allowing for its identification and measurement.
San Diego’s Wastewater Surveillance Program
San Diego has developed a wastewater surveillance program, involving a collaborative network of institutions. Partners include the University of California San Diego (UCSD), Scripps Research, and local public health departments. This collaboration, known as the San Diego Epidemiology and Research for COVID Health (SEARCH) program, supports the region’s monitoring efforts.
Samples are collected from major wastewater treatment facilities, such as the Point Loma, Encina, and South Bay Wastewater Treatment Plants, which collectively serve over 2.3 million residents. The program also expanded to include targeted sampling from specific sites like university campuses and K-8 schools. The frequency of collection varies, but samples from major treatment plants are collected multiple times per week or even daily to track viral trends.
What San Diego’s Wastewater Data Reveals
The concentration of SARS-CoV-2 viral RNA in wastewater reflects the prevalence of COVID-19 within a community. Higher concentrations of viral RNA indicate a greater number of infected individuals shedding the virus. Researchers can track trends in viral load, observing increases, decreases, or plateaus, which signal changes in community transmission.
This data provides an earlier signal of viral activity compared to traditional clinical case counts. Individuals shed the virus in their waste days before symptoms appear or before they seek clinical testing. Wastewater data is not influenced by testing availability or individual testing behaviors, offering a more complete picture of the virus’s spread, including undetected cases. The program can also sequence the wastewater to detect new SARS-CoV-2 variants, providing insights into the virus’s evolution.
Using Wastewater Data for Public Health in San Diego
San Diego’s public health officials integrate wastewater data with other metrics to inform their decision-making. This information complements data from hospitalizations, clinical testing, and genomic sequencing of individual patient samples. By combining these different data sources, public health authorities gain a more holistic understanding of the pandemic’s trajectory in the region.
The insights from wastewater monitoring help guide public health strategies, such as the allocation of resources for testing or vaccination campaigns to specific areas. It also assists in shaping public health messaging, allowing officials to communicate the current risk level to the community. While wastewater data provides valuable community-level insights, it is not used for individual diagnosis. Instead, it serves as a broad indicator of viral activity, helping San Diego respond to changes in COVID-19 prevalence.