Study Finds Dangerous Bacteria in Homes Plagued by Sewage Backups

A University of Maryland study of Baltimore houses with recent sewage backups revealed that most had toxic bacteria that could potentially infect residents who touch a contaminated surface or breathe contaminated air.

The 2022 pilot study found 34 of the 40 homes analyzed had at least one kind of harmful bacteria, some after more than six months following the sewage backup. Fourteen homes had more than one of the five pathogens studied. The researchers found bacteria resistant to standard antibiotics in seven homes. The latest findings in the multipart study were published last month in the Journal of Water & Health. 

Testing of one basement’s ankle-deep water detected E. coli at a concentration 10 times higher than the federal limit for lakes and other swimming areas, according to the study by UMD’s Water Emergency Team (WET). 

“We know intuitively that it's not good to have sewage in your home, but our work has now provided evidence that there are public health risks,” said study co-author Rachel E. Rosenberg Goldstein, Water Quality, Outreach and Wellness (WOW) Lab director and assistant professor of Global, Environmental, and Occupational Health.

Untreated sewage typically enters basements via drains, toilets and other plumbing fixtures when too much surface water or water leaking from stormwater pipes gets into cracked sewer pipes nearby. Sewer pipes also can get blocked from disposable personal wipes, cooking oil, tree roots and debris. 

While the problem of aging infrastructure in cities is well known, the UMD pilot study is believed to be the first to focus on the potential public health hazards of sewer backups into U.S. homes. Researchers said climate change has exacerbated the problem by bringing more of the heavy downpours that overwhelm aging systems. 

In Baltimore, where the sewer system dates to 1911, the city’s 311 service received 8,692 sewer-related complaints in the fiscal year ending June 30, according to a city report. 

Baltimore is required to fix the problem under a legal agreement, called a consent decree, with the U.S. Environmental Protection Agency, the U.S. Department of Justice and the Maryland Department of the Environment.

“When you plan for infrastructure services, you have to account for public health,” said Marccus Hendricks, an associate professor in the School of Architecture, Planning and Preservation and director of the Stormwater Infrastructure Resilience and Justice (SIRJ) Lab. “When you don't, you end up with the unexpected and unintended consequences of creating risk and potential contamination.”

The Baltimore pilot study was funded with $240,000 from Hendricks’ JPB Environmental Health Fellowship through the Harvard T.H. Chan School of Public Health. 

Faculty and students from UMD’s Water Emergency Team (WET) took swabs from basement floors and walls, as well as bathtubs, showers and kitchen sinks. 

One home had standing water with methicillin-resistant Staphylococcus aureus (MRSA), an antibiotic-resistant bacterium that the U.S. Centers For Disease Control and Prevention estimates causes more than 70,000 severe infections and 9,000 deaths annually. 

Researchers also tested for methicillin-susceptible S. aureus, coagulase-negative staphylococci (CoNS), methicillin-resistant CoNS  and E. coli, which signals fecal contamination and can cause a fever and gastrointestinal symptoms.

No residents reported being diagnosed with illnesses related to the five bacteria studied. However, some reported nausea (25%), shortness of breath (22.5%), fatigue (20%) and anxiety (65%). 

The pilot study’s findings are based on a relatively small number of homes, the researchers said. Because most were sampled weeks or even months after the sewage was gone, the studies also haven’t established direct links between the backups and bacteria found or health symptoms reported. 

However, Goldstein said the pilot study suggested a link because all 17 homes sampled within a month of a backup had at least one type of bacteria. Homes with more recent backups also were more likely to have pathogens than those where more time had passed. 

Since then, the research team has expanded its work into Prince George’s and Montgomery counties. Of 77 homes sampled there and in Baltimore between August 2023 and August 2024, 28 had antibiotic-resistant bacteria and 64 had bacteria indicating fecal contamination.

The ongoing research is being funded through a $2.2 million grant from the National Institutes of Health and a $1.3 million UMD Grand Challenges Grant. Detailed methodology and other findings have been published in Environmental Research: Health, PLOS Water and Environmental Research Communications; Assistant Research Professor Priscila B. R. Alves, the SIRJ Lab’s manager, was also a co-author.

As the project continues, the researchers plan to analyze the locations of sewer backups, saying they expect to find a disproportionate share occurring in underserved communities that have long received less infrastructure investment. 

Rita Crews, president of the Belair-Edison Community Association, one of the two Baltimore neighborhoods studied, said she hears about sewage-covered basements at least once a month. 

She said she hopes the UMD research leads to more funding to help residents, such as free home bacteria testing.

“It’s horrible,” Crews said of the basement backups. “In raw sewage, there’s all kinds of disease.”