Hospital sewers may be breeding grounds for dangerous superbugs, study finds

Antibiotics taken by patients can pass through their bodies and enter hospital sewer systems, creating conditions that favor the growth of resistant bacteria, according to the study. Antibiotic resistance occurs when bacteria develop the ability to survive drugs designed to kill them, making some infections harder to treat.

More than 9.3 million drug-resistant infections occur in the U.S. each year, resulting in more than 39,000 deaths, according to the CDC's 2026 Antimicrobial Resistance Threats Report.

Research methodology

The researchers conducted a study involving wastewater from 10 hospitals and eight municipal wastewater treatment plants. They wanted to determine whether hospital wastewater actually promoted the growth of antibiotic-resistant bacteria, rather than simply carrying resistant bacteria from patients.

First, the researchers filtered hospital wastewater to remove existing bacteria, then exposed other bacteria to the filtered water in laboratory experiments. All 10 hospital samples significantly favored the growth of E. coli strains resistant to ciprofloxacin and cefotaxime, two antibiotics used to treat bacterial infections.

None of the eight municipal wastewater samples showed the same effect. This suggested that something in the wastewater itself was helping antibiotic-resistant bacteria thrive, according to the researchers.

Findings

The team also placed plastic plates in sewer pipes to study bacteria growing on their surfaces. After 30 days, bacteria growing on surfaces inside the pipes were about three times as likely to be resistant to the two antibiotics as bacteria in the surrounding wastewater. This pattern was not observed in municipal sewers.

The researchers also measured antibiotic levels in the wastewater and tested whether those same concentrations helped resistant bacteria grow in laboratory experiments. They found that ciprofloxacin was a major contributor, while cefotaxime also played a role.

Potential solutions

The researchers identified two possible approaches to reducing antibiotic resistance in hospital sewers. One involves using alternative antibiotics that are less likely to pass through patients' bodies unchanged and promote the growth of resistant bacteria in wastewater.

The second approach involves treating wastewater at hospitals to remove antibiotics that promote resistance, particularly fluoroquinolones and beta-lactams, while also removing harmful bacteria. Larsson said treating wastewater at municipal plants would likely be less effective because antibiotic concentrations are high enough to favor resistant bacteria primarily in hospital sewers.

Existing technologies can remove antibiotics from wastewater, but they can be costly and require additional treatment. 'When we know more about the drivers, we think it might be possible to develop technical solutions that are targeted and hopefully less expensive,' Larsson added.