The SARS-CoV-2 pandemic has caused immeasurable suffering in terms of morbidity, mortality, and the effects of economic impacts, with vulnerable populations having been affected disproportionately. In particular, individuals residing in correctional facilities have suffered mortality rates above those of the comparable general population (Marquez et al., 2021); their vulnerabilities are associated with conditions in their communities (e.g., social determinants of health) as well as during confinement (Simpson and Butler, 2020). Specifically, SARS-CoV-2 is most efficiently transmitted in crowded, indoor spaces and the combination of environmental, resource, and organizational factors existent in corrections that facilitate SARS-CoV-2 transmission. At the same time, clinical testing of staff and residents to identify infections early and prevent transmission is challenging in correctional facilities (Hawks et al., 2020; Montoya-Barthelemy et al., 2020; Hassard et al., 2022).

In Massachusetts, approximately 6,500 individuals reside under the supervision of the Massachusetts Department of Correction (DOC) in a wide variety of facility sizes and infrastructure. Part of the DOC mission is to provide appropriate care for residents, and the DOC contracts with a private healthcare service (DOC Coronavirus Information Guide | Mass.gov) to meet those needs. In response to COVID-19, the DOC conducted activities to “minimize opportunities for the SARS-CoV-2 to enter state correctional facilities; to suppress its spread inside of those facilities; and to provide adequate testing to identify, and medical care to treat, residents and staff who contract it” (EOPSS and DOC, 2021).

Unfortunately, screening asymptomatic individuals is challenging because infection control interventions that follow the detection of a positive individual lead to testing refusals (Wurcel et al., 2020). In the absence of systematic screening, asymptomatic cases could easily go undetected and serve as sources of transmission. Because of this, the DOC implemented wastewater surveillance in select facilities in December 2020 with the vision to capture an unbiased sample of residents and use results to target testing and isolate positives early in the course of infection. Our objective was to quantify the correlation of COVID-19 cases with facility-level wastewater surveillance compared to standard case surveillance in towns in closest geographic proximity to participating correctional facilities.

We used several sources of data to measure cases for this study, including resident testing and case data from the DOC, the Massachusetts Department of Public Health surveillance system (Massachusetts Virtual Epidemiologic Network [MAVEN] case data from neighboring towns and surveillance notes), and Biobot Analytics (wastewater data).

Eight correctional facilities participated in wastewater surveillance (Table 1). The average daily population in 2021 at each facility ranged from < 100 residents to >1,000; facilities varied widely in terms of their security and resident demographics.

Between December 15, 2020 and February 12, 2022, a total of 1,246 COVID-19 cases were recorded across eight Massachusetts DOC facilities in residents, with 34,781 rapid antigen tests administered, 1,273 of which were positive. A total of 32,908 COVID-19 cases were recorded in the eight towns most closely geographically associated with each facility. In the same time frame, 890 wastewater samples were collected across all facilities (Table 1).

While wastewater surveillance has documented advantages for monitoring and controlling COVID-19 at the community (Gonzalez et al., 2020; Wu et al., 2022) and college-campus levels (Harris-Lovett et al., 2021; Wong et al., 2021), to our knowledge, this is the first study to quantify a relationship at correctional facilities. Furthermore, the case studies presented here document the application and direct utility of wastewater surveillance in a variety of correctional facility settings. Cases reported to routine surveillance, as captured in our town-level data, are affected by testing patterns and unless identified by screening, underestimate asymptomatic cases. Towns and correctional facilities have dynamic interactions in that staff and visitors frequently live in neighboring towns, and residents are released to towns (Montoya-Barthelemy et al., 2020; Hassard et al., 2022); however, this study found stronger correlations between wastewater surveillance at the correctional facilities and resident cases compared to town-level surveillance and resident cases.

A special feature of building-level wastewater surveillance for controlling COVID-19 is that it is actionable in a short feedback loop (Wong et al., 2021). New evidence indicates that it can also be affordable (Liu et al., 2022), which would allow further expansion in limited resource settings such as correctional facilities. In addition, since the programmatic efforts and costs of proactive clinical screening to detect infected individuals can be challenging (Brinkley-Rubinstein et al., 2021), our finding that wastewater monitoring at correctional facilities provides value beyond town- or city-level surveillance suggests this makes a good use case. The implementation of action in response to wastewater signals requires partnerships between public health and correctional facility leadership and staff. Wastewater surveillance in this setting can be an additional signal to aid infection control efforts at correctional facilities.

Evidence of town and resident case associations were described in a study of Massachusetts prisons where crowding was also a factor (Leibowitz et al., 2021). The movement of staff and visitors in and out of correctional facilities creates a challenge in interpretating wastewater data. Safety is a high priority of the Massachusetts DOC, and visits were managed. Additionally, as recommended by others (Hawks et al., 2020; Wang et al., 2020), an attempt to reduce the number of residents in 2020 was implemented to reduce COVID-19 transmission risk. Officials began dispensing the first round of doses of the COVID-19 vaccine for DOC residents and staff in January 2021 (EOPSS and DOC, 2021). However, there are many other barriers to controlling infection transmission in correctional facilities, including physical and structural challenges (Wang et al., 2020), and facilities have different capacities in implementing mitigation efforts.

Detection of SARS-CoV-2 in wastewater is an unequivocal result of infection somewhere. However, the many sources of variability in the detection of SARS-CoV-2 in wastewater (Wade et al., 2022) create challenges in interpretating individual results and frustrations for infection control. Smaller populations (i.e., building-level) under surveillance result in uncertainty in the quantitative correlation between wastewater concentrations and cases reported. The number of infected individuals who might contribute to the wastewater on a given day is hard to quantify; in addition, viral shedding in stool is highly variable from a single individual (Acer et al., 2022). As such, we caution partners to avoid overinterpreting a single observation of high concentrations of SARS-CoV-2 in wastewater. However, our observation that high viral concentration values were usually correlated with case clusters suggest a potential value in exploring guidance for interpretation based on certain cutoffs (e.g., percent increase). In addition, the availability and implementation of rapid, on-site testing have reduced the window of timing that wastewater offered earlier in the pandemic. This reinforces the value of combining these with other sources of surveillance data.

The greatest limitation of this study is the lack of biological evidence of infection in the population over time. Our data were observational and incomplete because our outcome (cases) underestimated infections for several reasons, including disincentives associated with the identification of a positive individual, inconsistent implementation of testing in response to wastewater signals, and undetected cases among staff and residents under mostly symptom-based testing. This means that the correlation analysis might not be ideal with cases as an outcome, and that our findings are conservative.

Formal model-based assessments of the cost benefit of using wastewater surveillance to monitor SARS-CoV-2 in correctional facilities are currently being evaluated through collaboration and support of CDC with a goal to develop an interactive tool similar to COVIDTracer and COVIDTracer Advanced | CDC.

The unique population vulnerabilities, along with environmental and structural conditions of correctional facilities that make clinical testing a challenge, suggest wastewater surveillance is beneficial in this setting. In Massachusetts, a partnership between DOC and DPH intends to expand wastewater surveillance to more facilities (EOPSS and DOC, 2021), and is consistent with CDC guidance on preventing transmission of SARS-CoV-2 in correctional facilities to include consideration for wastewater surveillance at the facility level (https://www.cdc.gov/coronavirus/2019-ncov/community/correction-detention/guidance-correctional-detention.html). Our findings of consistently higher correlation values between wastewater concentration and resident infections than town cases and resident infections offer robust support for conducting wastewater surveillance as an unbiased safety net of information about facilities where testing is challenging.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

RMK contributed to the conception of the work, interpretation of the data for the work, drafted and implemented revisions to the work, provided approval for publication of the content, and is accountable for all aspects of the work. CY and SO contributed to the design of the work, analysis and interpretation of the data for the work, drafted the work, provided approval for publication of the content, and is accountable for all aspects of the work. AO, DC, JM, LC, TS, and KC contributed substantially to the conception of the work, the acquisition and interpretation of data for the work, revision of the draft critically for important intellectual content, provided approval for publication of the content, and are accountable for all aspects of the work. All authors contributed to the article and approved the submitted version.