In its most basic form, SARS-CoV-2 monitoring involves collection of sewage samples at wastewater treatment facilities, where the sewage represents a pooled sample of the entire population served by the sewershed. There has also been significant interest expressed in more localized sewage monitoring to characterize specific communities, such as university campuses, or specific types of facilities, including dormitories, workplaces, prisons, and nursing homes. For all of these cases, it is important to consider the following additional questions:
- Is wastewater sampling an efficient and valuable use of resources? In other words, what specific benefit would wastewater sampling provide over other sampling options (e.g., direct clinical testing of all individuals or a random subset)? Depending on the size and characteristics of the facility, direct clinical testing may be more logistically or financially feasible and may provide more actionable information.
- How will the wastewater data be used? Is there a plan to integrate this data into the public health response? Wastewater sampling is not expected to stop an outbreak within a localized community or facility; however, it may identify an outbreak among that population, which should then be confirmed with additional testing data and managed appropriately. Prior to implementing wastewater monitoring, it is therefore important to devise an appropriate plan for additional action (e.g., clinical testing, contact tracing, isolating patients) upon receiving a positive wastewater sample result. Timely response to such data is likely critical in these cases; therefore, capacity for incorporating this data into data tracking and response workflows is an important consideration.
- How will the data be managed? Wastewater sampling at smaller, more localized facilities may be subject to additional privacy requirements and Institutional Review Board (IRB) approval. Additionally, reporting of such data can have a variety of public perception implications that should be considered. Collaboration with public health professionals who can advise on appropriate privacy protections is needed.
Additional specific considerations for these facilities are provided below.
Universities
University wastewater systems typically receive waste from all residential, non-residential, and laboratory facilities, and sometimes on-campus hospitals. The specific makeup of waste streams from each university will be campus-specific. Residential areas of campus may provide the most useful data as they are more likely to represent their respective populations. However, these areas are different from other “residential facilities” such as nursing homes and prisons (discussed below) in that dorm residents are free to leave their dorms and may defecate at other locations, and conversely, waste streams may include contributions from visitors in addition to residents. Despite this, targeting clusters of dormitories or residential areas of campus may be useful particularly as an early warning system. However, understanding the meaning of a positive SARS-CoV-2 detection in these areas and appropriate implications of this detection should be determined prior to the beginning of sampling.
Workplaces (e.g., food processing plants, distribution centers)
When collecting samples from workplaces, fecal matter containing viral RNA may not be captured from the entire population, depending on the habits of employees. Specifically, infected individuals may not defecate at their workplace, limiting the representativeness of wastewater monitoring at these locations. A short survey of employee habits may be useful in determining this. At food processing facilities or factories, industrial or food processing wastewater flows could dilute viral RNA signals, due to dilution by non-fecal waste streams. Food processing or industrial wastewaters can also contain large loads of organic material or other compounds that may inhibit molecular methods used to quantify viral RNA or interfere with typical processing controls, which would make analysis of samples challenging. For example, use of bovine coronavirus (BCoV) or bovine respiratory syncytial virus (BRSV) as an extraction control may be inappropriate for facilities that handle cattle, and validation of alternate controls would therefore be necessary.
Prisons
As opposed to university dorms and workplaces, prisons are residential facilities where inhabitants do not leave. Wastewater leaving a prison is guaranteed to capture fecal matter containing viral RNA from the entire incarcerated population. Some prisons operate their own on-site wastewater treatment plant. Privacy issues also need to be considered. We recommend consulting the appropriate IRB before planning any wastewater monitoring of prison populations.
Nursing homes
As residential facilities, nursing homes may serve as more useful targets for wastewater sampling than non-residential facilities & workplaces. This is because they are essentially guaranteed to capture fecal matter containing viral RNA from the entire population of residents, along with some workers. Sampling from nursing home wastewater may be especially valuable as an early warning system of a potential outbreak, as these facilities have been shown to be particularly dangerous for the spread of SARS-CoV-2. However, each facility should be evaluated separately; depending on population size and ease of sewer pipe access, clinical testing may be more appropriate.
