Boston Wastewater Monitoring

Wastewater includes everything that goes down a drain into a sewer. This includes the water people use to wash their hands, shower, use a toilet, or wash their clothes. 

A positive wastewater detection means at least one person with an active infection was in Boston shedding that virus into the sewer on the date the wastewater sample was drawn. This does not tell us how many people are infected or if they have any symptoms. This also does not tell us if the person(s) in question are still in Boston or if they were commuters, out-of-town patients, or visitors at large events.

However, even if the infected persons are no longer in Boston, the wastewater results indicate that local residents may have been exposed to the virus so we should still monitor closely for secondary cases. 

Wastewater monitoring acts as an early warning system, because it captures presence of a virus in sewage systems even before infected individuals may be symptomatic or diagnosed. It can also identify when a possible exposure may have occurred by infected visitors, even if those individuals no longer are in Boston. This early alert helps us inform other public health agencies, trigger response actions, and identify where diseases may be spreading before official diagnosed cases are reported by traditional clinical surveillance systems.

For example, BPHC’s ability to gather and share data about the number of COVID-19 infections decreased as at-home tests became more accessible and fewer clinical test results were reported. While not able to provide an exact number of infected people, wastewater data provides an alternative data source to track the relative level of disease spreading in a community. 

The disproportionate impact of the pandemic on vulnerable communities in Boston also illustrated that we need a better understanding of how specific communities are affected. Wastewater has proven useful during the pandemic for anticipating localized trends for respiratory illness like COVID-19. 

Wastewater data are community-level, anonymous, rapid, non-invasive, and do not rely on people having access to or seeking healthcare in order to know people are infected. Because people with diseases like COVID-19 often begin shedding virus in stool before developing symptoms, wastewater serves as an early indicator of cases. Wastewater data need to be considered along with other public health indicators, like the number of cases or hospitalizations, to truly understand the public health impact and risk of infectious disease trends, like those seen together on the BPHC Respiratory Illness Dashboard. 

Samples are collected twice weekly from 11 sewerholes in 10 neighborhoods throughout the city. The collected sewage is sent to GT Molecular's laboratories in Colorado. GT Molecular uses PCR, similar to the nasal swab tests clinics use to test people for COVID-19, to measure the amount of virus present in the wastewater.

When BPHC finds a virus in one of the wastewater samples, it means at least one person who was infected with the virus was in the neighborhood when the wastewater was collected.

The wastewater risk level reflects the amount of a virus present in the wastewater sample. A higher risk level indicates a higher amount of virus is present in recent samples.

For example, BPHC compared the first year of SARS-CoV-2 wastewater data to other COVID-19 indicators, and found that high levels of SARS-CoV-2 in wastewater correspond to high levels of COVID-19 outcomes, such as reported cases and hospitalizations.

An increasing trend means more virus was found in the wastewater compared to previous weeks, indicating more people may be infected. A decreasing trend means less virus was found in the wastewater, indicating fewer people may be infected.

Sites were selected with the goal of reaching as many of Boston’s neighborhoods as possible in order to have a representative snapshot of COVID transmission in the city. A citywide wastewater signal is calculated by taking a population-weighted average across these different sites. 

Wastewater data is similar to other public health indicators we have used throughout the pandemic to understand risk and make adjustments, such as test positivity and hospitalizations. Just as you would check your weather app to see if you need an umbrella to prevent yourself from getting rained on, checking wastewater data can be used to decide when to take more precautions to prevent infection. We have compiled guidance from BPHC and the US CDC for what actions you can take to prevent infection based on the wastewater level. 

Samples are collected twice weekly and this page is updated when data become available. 

Our network of sites will not include every person in Boston. These are meant to offer a snapshot across different areas of Boston to capture a citywide perspective. Everyone in Boston participates in wastewater surveillance, either through the BPHC program or through the MADPH surveillance of the Deer Island Treatment Plant, which collects wastewater from Boston and its surrounding suburbs. 

BPHC has developed a wastewater program to monitor disease trends within the city of Boston. Other sources of wastewater data, including data from the Deer Island Treatment Plant that treats wastewater from the Greater Boston Area, include contributions from surrounding communities, which can lead to different results. Other reasons these results may differ include: recent results may not be available, the laboratory that tests wastewater for BPHC may use different methods than laboratories testing wastewater for other organizations, and other organizations may use different methods to describe trends in their data.

In short, what BPHC publishes here is its best understanding of data from the BPHC Wastewater Monitoring Program. BPHC is not involved in producing or interpreting wastewater-related data coming from other sources.

Clinical guidance suggests that public health officials monitor for new measles cases for two incubation periods (6 weeks) after contact with an infected person. Because a positive detection of measles in wastewater means at least one person with an active measles infection was present in Boston on the date in question, even if the infected person is no longer in Boston, the wastewater results indicate that local residents may have been exposed. For this reason, BPHC monitors closely for new cases during this 6 week period.