Monitoring wastewater for the presence of infectious pathogens has a history of use in public health. For instance, wastewater monitoring has been used in the past in the surveillance and monitoring of polio virus. During the COVID-19 pandemic, it has been used for the detection and quantification of SARS-CoV-2 virus shed into wastewater via feces of infected persons. Wastewater surveillance tracks "pooled samples" that reflect the overall disease activity for a community serviced by the wastewater treatment plant (an area known as a "sewershed"), rather than tracking samples from individual people. Notably, while SARS-CoV-2 virus is shed fecally by infected persons, COVID-19 is spread primarily through the respiratory route, and there is no evidence to date that exposure to treated or untreated wastewater has led to infection with COVID-19.
Collecting and analyzing wastewater samples for the overall amount of SARS-CoV-2 viral particles present can help inform public health about the level of viral transmission within a community. Data from wastewater testing are not intended to replace existing COVID-19 surveillance systems, but are meant to complement them. While wastewater surveillance cannot determine the exact number of infected persons in the area being monitored, it can provide the overall trend of virus concentration within that community. This can be useful to public health for several key reasons:
Fecal shedding of SARS-CoV-2 virus can occur in infected individuals whether or not symptoms are present.
Approximately 90 percent of California households are served by municipal sewage collection systems.
Trends of SARS-CoV-2 measurements can provide information on changes in total COVID-19 infection in the community contributing to that sewershed.
Wastewater can provide data for communities where COVID-19 clinical testing is underutilized or experiencing limited access.