Household Contamination Sewage Overflows Linked to Drug-Resistant Bacteria in Homes

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Sewage overflows may bring more than unpleasant contamination into homes. A new study presented at ASM Microbe 2026 suggests that flooding and sewer backups can expose households to antibiotic-resistant and multidrug-resistant bacteria, raising public health concerns as ageing infrastructure and extreme weather increase the risk of such events.

A new study shows that sewage overflows in homes can expose people to bacteria that can make them sick, including antibiotic-resistant and multidrug resistant bacteria which can make infections difficult to treat. The research was presented at ASM Microbe 2026 in Washington, D.C.

“Our research underscores an urgent need to invest in upgrading water and sewer infrastructure to protect public health from this growing threat,” said corresponding study author Nick An, a Ph.D. candidate in the Department of Global, Environmental and Occupational Health at the School of Public Health at the University of Maryland, College Park.

Sewage overflows are an ongoing issue in the city of Baltimore, throughout Maryland, across the U.S., and globally. They occur when untreated sewage enters homes or the environment through broken, clogged or overwhelmed pipes. Although this issue is well documented, there is limited information on the public health risks from sewage overflows and flooding in impacted homes.

In the new study, the research team collected 107 samples from 86 Maryland homes between October 2023 and June 2025. The team analyzed these samples for Enterococci bacteria commonly used as indicators for fecal contamination. The researchers also determined if a range of antibiotics were effective, or not, against these bacteria.

The researchers found that nearly half (46%) of the homes had Enterococci present. Additionally, 21% of homes had E. faecalis and 27% E. faecium present, specific species of Enterococci that can cause infections, especially in those with weakened immune systems. More homes where sewage or water events had occurred within the past month had Enterococci present compared to homes without recent events, suggesting that timing may play an important role in being exposed to these bacteria.

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Additionally, the study found antibiotic-resistant Enterococci, bacteria that can no longer be treated with certain antibiotics, in over a third of the homes. More than 1 in 10 homes harbored multidrug resistant Enterococci, bacteria resistant to 3 or more antibiotic classes. When bacteria become resistant to multiple antibiotics, infections can become even more difficult to treat as effective treatments are more limited. Homes with recent sewage or water events had 3 times more multidrug resistant bacteria present compared to homes without recent events, although it cannot be ruled out that this difference was due to chance, given the study's size.

The study suggests that sewage overflows and flooding could introduce antibiotic-resistant bacteria into homes. As extreme weather events become more frequent and sewer systems continue to age, more households could be exposed to these disease-causing organisms.

The researchers plan to collect additional samples from homes impacted by sewage overflows and flooding throughout the summer and analyze samples for target bacteria. “We also plan to share our findings at community events in neighborhoods we have worked in and more broadly in Maryland communities impacted by sewage overflows,” An said.

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