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

Hospital wastewater promotes the growth of antibiotic-resistant bacteria, potentially making hospital sewer systems hotspots for antimicrobial resistance, according to a new Swedish study published in Nature Communications.

According to the study, antibiotics taken by patients can pass through their bodies and enter hospital sewer systems, creating conditions that favour the growth of resistant bacteria. 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 United States each year, resulting in more than 39,000 deaths, according to the CDC's 2026 Antimicrobial Resistance Threats Report.

The researchers studied 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 favoured 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.

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.

Joakim Larsson, professor of environmental pharmacology at the University of Gothenburg and director of the Centre for Antibiotic Resistance Research, told Fox News Digital, 'The discovery suggests that hospital sewers could be a spawning ground for bacteria that are difficult to treat with antibiotics.'

Larsson said, 'Knowing where resistant bacteria are promoted — and where they are less likely to be — is crucial when deciding how resources and efforts should be allocated to limit risks for antibiotic resistance development.'

The study had several limitations. All sampling sites were in Sweden, and researchers focused primarily on E. coli and a limited number of antibiotics, so the findings may not apply to all bacteria or locations. The sewer experiment lasted approximately 30 days, leaving longer-term effects unclear. The study also did not determine whether the growth of resistant bacteria in hospital sewers leads to more infections in patients or surrounding communities.

Although the study did not directly link hospital wastewater to human infections, Larsson said resistant bacteria could potentially reach people through contaminated water. He said, 'When it rains heavily, treatment plants are typically overloaded, and release untreated or partially untreated wastewater with lots of bacteria. If people get in contact with such waters, they can acquire those bacteria and then continue spreading them from person to person.'

The researchers identified two possible approaches to reducing resistance in hospital sewers. One involves using alternative antibiotics that are less likely to pass through patients' bodies unchanged and promote resistant bacteria in wastewater. But Larsson emphasised that patients' need for antibiotics must not be compromised, and equally effective alternatives may not always be available.

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 favour resistant bacteria primarily in hospital sewers. Existing technologies can remove antibiotics from wastewater, but they can be costly and require additional treatment, he noted.