Hidden Epidemic: Drug-Resistant Bacteria Are Spreading Through Hospital Plumbing

A study found that hospital sink drains harbor dangerous bacteria, including antibiotic-resistant strains.

Despite thorough cleaning, bacteria persist and spread, posing risks to vulnerable patients. Some strains even resist last-resort antibiotics, highlighting a major public health concern.

Deadly Infections Lurking in Hospitals

When we go to the hospital, we expect to get better — not to leave with a new infection. Yet, healthcare-associated infections (HAIs) are a growing global problem, consuming an estimated 6% of hospital budgets worldwide. In the European Union alone, HAIs lead to over 3.5 million cases annually, causing 2.5 million disability-adjusted life years, costing up to €24 billion (~$25 billion), and contributing to 90,000 deaths. In the United States, they rank as the sixth leading cause of death.

HAIs spread more easily in patients with weakened immune systems and in hospitals where hygiene protocols are not strictly followed. Additionally, the widespread use of antibiotics in hospitals promotes the survival of resistant bacteria. When these bacteria carry resistance genes on mobile genetic elements, they can transfer those traits to other bacterial species, increasing the risk of new and potentially more dangerous infections.

Bacteria Hiding in Hospital Sinks

“Here we show that hospital sink drains host bacterial populations that change over time, despite impeccable cleaning protocols in the particular hospital we looked at,” said Dr. Margarita Gomila, a professor at the University of the Balearic Islands in Spain, and the senior author of a study in Frontiers in Microbiology.

“These results highlight that controlling bacterial growth in drains, and preventing colonization by new strains of such hard-to-disinfect niches, is likely a global problem.”

Rigorous Cleaning Protocols, But Are They Enough?

Gomila and her coworkers focused on sink drains in a single modern university hospital on the island of Majorca, built in 2001 and managed by the health service of the Balearic Islands. Cleaning protocols there are state-of-the-art: sinks and their drains are routinely cleaned with bleach, as well as disinfected with chemicals and pressurized steam every fortnight, or every month in non-patient areas. Once a year, drainpipes are hyperchlorinated at low temperatures.

Four times between February 2022 and February 2023, they used cotton swabs to sample six drains in each of five wards: two for intensive care, including a brand-new one; one ward each for hematology, short stays, and general medicine; as well as a microbiology laboratory. They cultured the sampled bacteria on five different media and at two different temperatures, and identified the resulting 1,058 isolates with DNA barcoding and mass spectrometry. They then used an automated platform to test whether each of the 219 isolates was resistant to a range of antibiotics.

Diverse and Persistent Bacterial Colonies

The authors identified a total of 67 different species from the drains. The diversity in most drains went up and down over time with no clear pattern – seasonal or otherwise. The greatest diversity occurred in general medicine and intensive care, while the fewest isolates were found in the microbiology laboratory. Strikingly, the new intensive care unit, which opened in July 2022, already showed a high level of bacterial diversity from the opening, on a par with its longer-established twin.

The Most Dangerous Pathogens Found

Dominant across wards were six Stenotrophomonas species as well as Pseudomonas aeruginosa, a pathogen known to cause ventilator-associated pneumonia and sepsis, and characterized by the WHO as one of the greatest threats to humans in terms of antibiotic resistance. At least 16 other Pseudomonas species were also found at various times and in various wards, but especially in the short-stay ward.

Other notorious hospital-associated pathogens found repeatedly were Klebsiella pneumoniae in the general medicine ward, Acinetobacter johnsonii and Acinetobacter ursingii in general medicine and intensive care, Enterobacter mori and Enterobacter quasiroggenkampii in the short-stay ward, and Staphylococcus aureus in intensive care and hematology.

“The bacteria we found may originate from many sources, from patients, medical personnel, and even the environment surrounding the hospital. Once established in sink drains, they can spread outwards, posing significant risks to immunocompromised patients above all,” said Gomila.

Antibiotic Resistance: A Growing Concern

Of the species found here, Klebsiella, Enterobacter, and P. aeruginosa feature among the so-called ESKAPE group of bacteria, known to thrive in hospital settings and to show frequent multi-resistance and a high potential for causing illness.

In the present study, 21% of P. aeruginosa isolates were found to be resistant to at least one class of antibiotics. Multiple Klebsiella and Enterobacter strains detected proved resistant to the third-generation antibiotic cephalosporin, but not to the carbapenems commonly used today against multidrug-resistant infections.

Worryingly, the blaVIM gene, which makes its carriers resistant even to carbapenems, was detected sporadically in a minority of P. aeruginosa strains from the two intensive care wards, the general medicine ward, and the short-stay ward.

Hospital Drains: A Hidden Reservoir of Superbugs

The authors concluded that hospital drains can serve as reservoirs for both known and emerging pathogens, some of which exhibit strong antibiotic resistance.

“Cleaning protocols are important and should be frequently applied, especially in wards that are kept separate precisely to slow the spread of potentially harmful bacteria. But to get to the bottom of the problem, it’s essential to study the source of these bacteria and their routes of transmission,” reminded first author José Laço, a PhD student in Gomila’s laboratory.

Reference: “Yearlong analysis of bacterial diversity in hospital sink drains: culturomics, antibiotic resistance and implications for infection control” by José Laço, Sergi Martorell, Maria del Carmen Gallegos and Margarita Gomila, 18 November 2024, Frontiers in Microbiology.