Sewage overflows are linked to an increase in gastrointestinal diseases

During extreme rain or rapid snowmelt, the large amount of water entering sewers can cause untreated sewage to enter waterways in U.S. cities that have a combined wastewater and stormwater sewer system, including the Merrimack River in Massachusetts.

A new study led by researchers at Boston University School of Public Health (BUSPH) has found that residents living in the downstream communities bordering the Merrimack River are at significantly increased risk of developing acute gastrointestinal illness ( AGI) in the four days after the major illness. volume of combined sewer overflows (CSOs).

Published in the magazine Environmental health perspectivesThe study found that the risk of AGI was elevated among all Massachusetts towns observed in the analysis, regardless of whether the communities got their drinking water from the Merrimack River, suggesting that residents may be exposed to sewage-related contaminants through other pathways then just drink. water.

Health experts are concerned that more extreme rainfall due to climate change will spur additional large-scale civil society activities, further endangering the health of residents.

“The greatest sewage emissions occur when precipitation is most intense, as this causes a large amount of rainfall in a short period of time,” said study leader and corresponding author Dr. Beth Haley, postdoctoral researcher and then PhD student at BUSPH. of the study.

“Our findings are concerning because climate change predictions suggest that heavy rainfall will become more frequent and intense in the Northeast, meaning residents of communities exposed to sewage-contaminated waterways may experience an increased risk of serious gastrointestinal illness.”

The study provides critical insight into the health impacts of CSOs, as very little research has examined the health outcomes of populations exposed to the waterways CSOs impact. The analysis is also the first study to examine the role of drinking water sources in these potential connections between CSOs and AGI.

For the study, Dr. Haley and colleagues from Boston University, the University of Chicago, and New Leaf Energy used federal and state data to examine the volume and intensity of community organizations, along with hospital data of emergency room visits for AGI, by diagnoses. of infectious intestinal diseases, non-infectious gastroenteritis, vomiting and diarrhea. The analysis included communities in all 17 northern Massachusetts cities bordering the Merrimack River.

After adjusting for precipitation, results showed that residents living in CSO-affected communities were 62% more likely to develop AGI within four days after the largest sewage overflow occurred in the study period, compared to days without CSO events. But there was no meaningful difference in AGI risk based on whether residents relied on drinking water from the Merrimack River or other sources.

Exposure to sewage-associated pathogens in drinking water is of particular concern because of the large number of people who rely on public drinking water, the researchers say. a relief. But they are careful to note that the results do not necessarily indicate that drinking water from waterways affected by the CSO is harmless.

“We cannot conclude that drinking water is not a route of exposure following CSO events, but this study does suggest that other routes, for example exposure during water recreation, are likely to contribute more to the observed association,” says Dr. Haley.

More research is needed to better understand the role of drinking water on CSO-associated AGI risk, especially for populations more susceptible to microbial pathogens, such as immunocompromised people, the elderly and young children, the team says.

Although cities such as San Francisco, Seattle, and Portland, Oregon, have combined sewer systems, this type of infrastructure is more common in the Northeast and Midwest, where systems were built in the nation’s oldest cities in the mid-19th to early 20th centuries.

“At the time, there was little concern that combining sanitary and storm sewers would be so problematic,” says senior study author Dr. Wendy Heiger-Bernays, clinical professor of environmental health at BUSPH. One of the main reasons why community events still occur today, she says, is that combined sewer systems are expensive to separate, as are measures to minimize community events.

“Many cities with combined sewer systems do not have the resources to make these major infrastructure investments without state or federal assistance.”

There is now some movement to address these issues at the federal level, Heiger-Bernays says. The Environmental Protection Agency (EPA) is work to implement long-term monitoring plans and water quality improvements – and to make CSO data more easily available to the public – in accordance with the Clean Water Act.

“Massachusetts has done this at the state level after the passage of a Law 2021 which requires reporting of sewer overflow events, but a national system for reporting and data access does not currently exist,” she says.